===================================================================
--- original.js
+++ change.js
@@ -1,6 +1,715 @@
-/****
+/**** 
+* Plugins
+****/ 
+var tween = LK.import("@upit/tween.v1");
+var storage = LK.import("@upit/storage.v1", {
+	level: 1,
+	collectedKeys: 0,
+	lives: 3
+});
+
+/**** 
+* Classes
+****/ 
+var Door = Container.expand(function () {
+	var self = Container.call(this);
+	var doorGraphics = self.attachAsset('door', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.isLocked = true;
+	self.unlock = function () {
+		self.isLocked = false;
+		tween(doorGraphics, {
+			alpha: 0.3
+		}, {
+			duration: 500
+		});
+		LK.getSound('unlockDoor').play();
+	};
+	return self;
+});
+var Explorer = Container.expand(function () {
+	var self = Container.call(this);
+	var explorerGraphics = self.attachAsset('explorer', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.speed = 10;
+	self.isMoving = false;
+	self.direction = null;
+	self.targetX = 0;
+	self.targetY = 0;
+	self.hasKey = false;
+	self.moveToward = function (x, y) {
+		self.isMoving = true;
+		self.targetX = x;
+		self.targetY = y;
+		// Calculate direction
+		var dx = self.targetX - self.x;
+		var dy = self.targetY - self.y;
+		// Determine primary direction based on larger delta
+		if (Math.abs(dx) > Math.abs(dy)) {
+			self.direction = dx > 0 ? 'right' : 'left';
+		} else {
+			self.direction = dy > 0 ? 'down' : 'up';
+		}
+	};
+	self.stopMoving = function () {
+		self.isMoving = false;
+		self.direction = null;
+	};
+	self.update = function () {
+		if (self.isMoving) {
+			var dx = self.targetX - self.x;
+			var dy = self.targetY - self.y;
+			var distance = Math.sqrt(dx * dx + dy * dy);
+			if (distance < self.speed) {
+				self.x = self.targetX;
+				self.y = self.targetY;
+				self.stopMoving();
+			} else {
+				var ratio = self.speed / distance;
+				self.x += dx * ratio;
+				self.y += dy * ratio;
+			}
+		}
+	};
+	self.collectKey = function () {
+		self.hasKey = true;
+		tween(explorerGraphics, {
+			tint: 0xFFD700
+		}, {
+			duration: 300,
+			onFinish: function onFinish() {
+				tween(explorerGraphics, {
+					tint: 0xFFFFFF
+				}, {
+					duration: 300
+				});
+			}
+		});
+	};
+	self.useKey = function () {
+		self.hasKey = false;
+		storage.collectedKeys++;
+	};
+	self.takeDamage = function () {
+		LK.effects.flashObject(self, 0xFF0000, 500);
+		storage.lives--;
+		LK.getSound('damage').play();
+		if (storage.lives <= 0) {
+			LK.showGameOver();
+		}
+	};
+	return self;
+});
+var FallingRock = Container.expand(function () {
+	var self = Container.call(this);
+	var rockGraphics = self.attachAsset('rock', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.isTriggered = false;
+	self.isFalling = false;
+	self.initialY = 0;
+	self.fallSpeed = 0;
+	self.resetTimer = 0;
+	self.resetDelay = 180; // 3 seconds
+	self.trigger = function () {
+		if (!self.isTriggered && !self.isFalling) {
+			self.isTriggered = true;
+			self.fallSpeed = 2; // Start with slow fall
+			// Shake before falling
+			tween(rockGraphics, {
+				x: 5
+			}, {
+				duration: 100,
+				onFinish: function onFinish() {
+					tween(rockGraphics, {
+						x: -5
+					}, {
+						duration: 100,
+						onFinish: function onFinish() {
+							tween(rockGraphics, {
+								x: 0
+							}, {
+								duration: 100,
+								onFinish: function onFinish() {
+									self.isFalling = true;
+									self.isTriggered = false;
+								}
+							});
+						}
+					});
+				}
+			});
+		}
+	};
+	self.reset = function () {
+		self.y = self.initialY;
+		self.isFalling = false;
+		self.fallSpeed = 0;
+		self.resetTimer = 0;
+	};
+	self.update = function () {
+		if (self.isFalling) {
+			self.fallSpeed += 0.2; // Acceleration
+			self.y += self.fallSpeed;
+			// Check if rock has fallen out of view
+			if (self.y > 2832) {
+				self.isFalling = false;
+				self.resetTimer = 0;
+			}
+		} else if (self.y !== self.initialY) {
+			// Reset timer
+			self.resetTimer++;
+			if (self.resetTimer >= self.resetDelay) {
+				self.reset();
+			}
+		}
+	};
+	return self;
+});
+var Key = Container.expand(function () {
+	var self = Container.call(this);
+	var keyGraphics = self.attachAsset('key', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.update = function () {
+		// Float animation
+		keyGraphics.y = Math.sin(LK.ticks / 20) * 5;
+		// Rotate slowly
+		keyGraphics.rotation += 0.01;
+	};
+	return self;
+});
+var River = Container.expand(function () {
+	var self = Container.call(this);
+	var riverGraphics = self.attachAsset('river', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.hasBridge = false;
+	self.addBridge = function () {
+		if (!self.hasBridge) {
+			var bridge = self.attachAsset('bridge', {
+				anchorX: 0.5,
+				anchorY: 0.5
+			});
+			self.hasBridge = true;
+			return bridge;
+		}
+	};
+	self.update = function () {
+		// Flowing water animation
+		riverGraphics.tint = 0x1E88E5 + Math.floor(Math.sin(LK.ticks / 20) * 20) * 0x000101;
+	};
+	return self;
+});
+var Spike = Container.expand(function () {
+	var self = Container.call(this);
+	var spikeGraphics = self.attachAsset('spike', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.isActive = false;
+	self.timer = 0;
+	self.cycleTime = 120; // 2 seconds at 60fps
+	self.update = function () {
+		self.timer++;
+		if (self.timer >= self.cycleTime) {
+			self.timer = 0;
+			self.isActive = !self.isActive;
+			if (self.isActive) {
+				tween(spikeGraphics, {
+					scaleY: 1
+				}, {
+					duration: 300
+				});
+			} else {
+				tween(spikeGraphics, {
+					scaleY: 0.2
+				}, {
+					duration: 300
+				});
+			}
+		}
+	};
+	// Initialize in retracted state
+	spikeGraphics.scaleY = 0.2;
+	return self;
+});
+var Treasure = Container.expand(function () {
+	var self = Container.call(this);
+	var treasureGraphics = self.attachAsset('treasure', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.isCollected = false;
+	self.collect = function () {
+		if (!self.isCollected) {
+			self.isCollected = true;
+			tween(treasureGraphics, {
+				scaleX: 1.3,
+				scaleY: 1.3
+			}, {
+				duration: 300,
+				onFinish: function onFinish() {
+					tween(treasureGraphics, {
+						scaleX: 0,
+						scaleY: 0
+					}, {
+						duration: 300
+					});
+				}
+			});
+			LK.setScore(LK.getScore() + 100);
+			LK.getSound('collectTreasure').play();
+			// Check if all treasures are collected
+			var allCollected = true;
+			for (var i = 0; i < treasures.length; i++) {
+				if (!treasures[i].isCollected) {
+					allCollected = false;
+					break;
+				}
+			}
+			if (allCollected) {
+				// Level complete
+				storage.level++;
+				LK.showYouWin();
+			}
+		}
+	};
+	self.update = function () {
+		if (!self.isCollected) {
+			// Shine animation
+			var glowIntensity = (Math.sin(LK.ticks / 30) + 1) / 2;
+			treasureGraphics.alpha = 0.7 + glowIntensity * 0.3;
+		}
+	};
+	return self;
+});
+var Wall = Container.expand(function () {
+	var self = Container.call(this);
+	var wallGraphics = self.attachAsset('wall', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	return self;
+});
+
+/**** 
 * Initialize Game
-****/
+****/ 
 var game = new LK.Game({
-	backgroundColor: 0x000000
-});
\ No newline at end of file
+	backgroundColor: 0x607D8B // Cave-like dark blue-gray
+});
+
+/**** 
+* Game Code
+****/ 
+// Game variables
+var tileSize = 100;
+var gridWidth = 20;
+var gridHeight = 27;
+var explorer;
+var walls = [];
+var keys = [];
+var doors = [];
+var treasures = [];
+var spikes = [];
+var fallingRocks = [];
+var rivers = [];
+var bridges = [];
+var levelGrid = [];
+var gameStarted = false;
+// UI Elements
+var scoreTxt = new Text2('0', {
+	size: 80,
+	fill: 0xFFFFFF
+});
+var levelTxt = new Text2('Level: ' + storage.level, {
+	size: 60,
+	fill: 0xFFFFFF
+});
+var keysTxt = new Text2('Keys: ' + storage.collectedKeys, {
+	size: 60,
+	fill: 0xFFD700
+});
+var livesTxt = new Text2('Lives: ' + storage.lives, {
+	size: 60,
+	fill: 0xFF5252
+});
+// Initialize game
+function initializeGame() {
+	// Clear previous game elements
+	resetGameElements();
+	// Generate level based on current level
+	generateLevel(storage.level);
+	// Initialize explorer
+	createExplorer();
+	// Setup UI
+	setupUI();
+	// Start game
+	gameStarted = true;
+	// Play background music
+	LK.playMusic('caveMusic', {
+		fade: {
+			start: 0,
+			end: 0.3,
+			duration: 1000
+		}
+	});
+}
+function resetGameElements() {
+	// Remove all existing game elements
+	for (var i = 0; i < walls.length; i++) {
+		walls[i].destroy();
+	}
+	walls = [];
+	for (var i = 0; i < keys.length; i++) {
+		keys[i].destroy();
+	}
+	keys = [];
+	for (var i = 0; i < doors.length; i++) {
+		doors[i].destroy();
+	}
+	doors = [];
+	for (var i = 0; i < treasures.length; i++) {
+		treasures[i].destroy();
+	}
+	treasures = [];
+	for (var i = 0; i < spikes.length; i++) {
+		spikes[i].destroy();
+	}
+	spikes = [];
+	for (var i = 0; i < fallingRocks.length; i++) {
+		fallingRocks[i].destroy();
+	}
+	fallingRocks = [];
+	for (var i = 0; i < rivers.length; i++) {
+		rivers[i].destroy();
+	}
+	rivers = [];
+	for (var i = 0; i < bridges.length; i++) {
+		bridges[i].destroy();
+	}
+	bridges = [];
+	levelGrid = [];
+	if (explorer) {
+		explorer.destroy();
+		explorer = null;
+	}
+}
+function createExplorer() {
+	explorer = new Explorer();
+	game.addChild(explorer);
+	// Position explorer at start position
+	for (var y = 0; y < gridHeight; y++) {
+		for (var x = 0; x < gridWidth; x++) {
+			if (levelGrid[y][x] === 'S') {
+				explorer.x = x * tileSize + tileSize / 2;
+				explorer.y = y * tileSize + tileSize / 2;
+				break;
+			}
+		}
+	}
+}
+function setupUI() {
+	// Setup score text
+	scoreTxt.setText(LK.getScore());
+	scoreTxt.anchor.set(1, 0);
+	LK.gui.topRight.addChild(scoreTxt);
+	// Setup level text
+	levelTxt.setText('Level: ' + storage.level);
+	levelTxt.anchor.set(0.5, 0);
+	levelTxt.y = 80;
+	LK.gui.top.addChild(levelTxt);
+	// Setup keys text
+	keysTxt.setText('Keys: ' + storage.collectedKeys);
+	keysTxt.anchor.set(0, 0);
+	keysTxt.y = 80;
+	LK.gui.topRight.addChild(keysTxt);
+	// Setup lives text
+	livesTxt.setText('Lives: ' + storage.lives);
+	livesTxt.anchor.set(0, 0);
+	LK.gui.topRight.addChild(livesTxt);
+}
+function generateLevel(level) {
+	// Define different level layouts
+	var layouts = [];
+	// Level 1: Simple tutorial level
+	layouts[1] = ["WWWWWWWWWWWWWWWWWWWW", "W        W         W", "W WWWWWW W WWWWWWW W", "W W           K  W W", "W W WWWWWWWWWWWW W W", "W W W            W W", "W W W WWWWWWWWWW W W", "W W W W        W W W", "W W W W WWWWWW W W W", "W W W W W    W W W W", "W W W W W WW W W W W", "W W   W W  W   W W W", "W WWWWW WWWWWWWW W W", "W                W W", "W WWWWWWWWWWWWWWWW W", "W                  W", "W WWWWWWWW WWWWWWW W", "W W      W       W W", "W W WWWW WWWWWWW W W", "W W W           W W W", "W W W WWWWWWWWW W W W", "W W W         W W W W", "W W WWWWWWWWW W W W W", "W W        DW W W W W", "W WWWWWWWWWWW W W TS W", "W              W    W", "WWWWWWWWWWWWWWWWWWWWW"];
+	// Level 2: Introducing spikes
+	layouts[2] = ["WWWWWWWWWWWWWWWWWWWW", "W        W         W", "W WWWWWW W WWWWWWW W", "W W           K  W W", "W W WWWWWWWWWWWW W W", "W W W            W W", "W W W WWWWWWWWWW W W", "W W W W        W W W", "W W W W WWWWWW W W W", "W W W W W    W W W W", "W W W W W WW W W W W", "W W   W W  W   W W W", "W WWWWW WWWWWWWW W W", "W         X     W W W", "W WWWWWWWWWWWWWWWW W", "W     X      X     W", "W WWWWWWWW WWWWWWW W", "W W      W       W W", "W W WWWW WWWWWWW W W", "W W W     X     W W W", "W W W WWWWWWWWW W W W", "W W W    X    W W W W", "W W WWWWWWWWW W W W W", "W W        DW W W W W", "W WWWWWWWWWWW W W TS W", "W              W    W", "WWWWWWWWWWWWWWWWWWWWW"];
+	// Level 3: Introducing falling rocks
+	layouts[3] = ["WWWWWWWWWWWWWWWWWWWW", "W        W         W", "W WWWWWW W WWWWWWW W", "W W           K  W W", "W W WWWWWWWWWWWW W W", "W W W     F      W W", "W W W WWWWWWWWWW W W", "W W W W  F     W W W", "W W W W WWWWWW W W W", "W W W W W    W W W W", "W W W W W WW W W W W", "W W   W W  W   W W W", "W WWWWW WWWWWWWW W W", "W    F    X     W W W", "W WWWWWWWWWWWWWWWW W", "W     X  F   X     W", "W WWWWWWWW WWWWWWW W", "W W      W       W W", "W W WWWW WWWWWWW W W", "W W W     X  F  W W W", "W W W WWWWWWWWW W W W", "W W W F  X    W W W W", "W W WWWWWWWWW W W W W", "W W        DW W W W W", "W WWWWWWWWWWW W W TS W", "W              W    W", "WWWWWWWWWWWWWWWWWWWWW"];
+	// Level 4: Introducing rivers
+	layouts[4] = ["WWWWWWWWWWWWWWWWWWWW", "WS       W         W", "W WWWWWW W WWWWWWW W", "W W           K  W W", "W W WWWWWWWWWWWW W W", "W W W     F      W W", "W W W WWWWWWWWWW W W", "W W W W  F     W W W", "W W W W WWWWWW W W W", "W W W W W    W W W W", "W W W W W WW W W W W", "W W   W W  W   W W W", "W WWWWW WWWWWWWW W W", "W    F    X     W W W", "WRRRRRRRRRRRRRRRRR W", "W     X  F   X     W", "W WWWWWWWW WWWWWWW W", "W W      W       W W", "W W WWWW WWWWWWW W W", "W W W     X  F  W W W", "W W W WWWWWWWWW W W W", "W W W F  X    W W W W", "W W WWWWWWWWW W W W W", "W W        DW W W W W", "W WWWWWWWWWWW W W T  W", "W              W    W", "WWWWWWWWWWWWWWWWWWWWW"];
+	// Get layout for current level or use level 4 for any higher levels
+	var currentLayout = layouts[Math.min(level, 4)];
+	// Parse level layout
+	for (var y = 0; y < currentLayout.length; y++) {
+		levelGrid[y] = [];
+		for (var x = 0; x < currentLayout[y].length; x++) {
+			var cellType = currentLayout[y][x];
+			levelGrid[y][x] = cellType;
+			var xPos = x * tileSize + tileSize / 2;
+			var yPos = y * tileSize + tileSize / 2;
+			switch (cellType) {
+				case 'W':
+					// Wall
+					var wall = new Wall();
+					wall.x = xPos;
+					wall.y = yPos;
+					game.addChild(wall);
+					walls.push(wall);
+					break;
+				case 'K':
+					// Key
+					var key = new Key();
+					key.x = xPos;
+					key.y = yPos;
+					game.addChild(key);
+					keys.push(key);
+					break;
+				case 'D':
+					// Door
+					var door = new Door();
+					door.x = xPos;
+					door.y = yPos;
+					game.addChild(door);
+					doors.push(door);
+					break;
+				case 'T':
+					// Treasure
+					var treasure = new Treasure();
+					treasure.x = xPos;
+					treasure.y = yPos;
+					game.addChild(treasure);
+					treasures.push(treasure);
+					break;
+				case 'X':
+					// Spike trap
+					var spike = new Spike();
+					spike.x = xPos;
+					spike.y = yPos;
+					game.addChild(spike);
+					spikes.push(spike);
+					break;
+				case 'F':
+					// Falling rock
+					var rock = new FallingRock();
+					rock.x = xPos;
+					rock.y = yPos;
+					rock.initialY = yPos;
+					game.addChild(rock);
+					fallingRocks.push(rock);
+					break;
+				case 'R':
+					// River
+					var river = new River();
+					river.x = xPos;
+					river.y = yPos;
+					game.addChild(river);
+					rivers.push(river);
+					break;
+			}
+		}
+	}
+}
+function getGridPosition(x, y) {
+	var gridX = Math.floor(x / tileSize);
+	var gridY = Math.floor(y / tileSize);
+	if (gridX >= 0 && gridX < gridWidth && gridY >= 0 && gridY < gridHeight) {
+		return {
+			x: gridX,
+			y: gridY
+		};
+	}
+	return null;
+}
+function isWalkable(gridX, gridY) {
+	if (gridX < 0 || gridX >= gridWidth || gridY < 0 || gridY >= gridHeight) {
+		return false;
+	}
+	var cellType = levelGrid[gridY][gridX];
+	// Check if cell is walkable
+	if (cellType === 'W') {
+		return false;
+	}
+	// Check if door is locked
+	if (cellType === 'D') {
+		var door = getDoorAt(gridX, gridY);
+		return door && !door.isLocked;
+	}
+	// Check if river has bridge
+	if (cellType === 'R') {
+		var river = getRiverAt(gridX, gridY);
+		return river && river.hasBridge;
+	}
+	return true;
+}
+function getDoorAt(gridX, gridY) {
+	for (var i = 0; i < doors.length; i++) {
+		var doorPos = getGridPosition(doors[i].x, doors[i].y);
+		if (doorPos && doorPos.x === gridX && doorPos.y === gridY) {
+			return doors[i];
+		}
+	}
+	return null;
+}
+function getRiverAt(gridX, gridY) {
+	for (var i = 0; i < rivers.length; i++) {
+		var riverPos = getGridPosition(rivers[i].x, rivers[i].y);
+		if (riverPos && riverPos.x === gridX && riverPos.y === gridY) {
+			return rivers[i];
+		}
+	}
+	return null;
+}
+// Update UI
+function updateUI() {
+	scoreTxt.setText(LK.getScore());
+	levelTxt.setText('Level: ' + storage.level);
+	keysTxt.setText('Keys: ' + storage.collectedKeys);
+	livesTxt.setText('Lives: ' + storage.lives);
+}
+// Check for collisions
+function checkCollisions() {
+	if (!explorer) {
+		return;
+	}
+	var explorerPos = getGridPosition(explorer.x, explorer.y);
+	if (!explorerPos) {
+		return;
+	}
+	var cellType = levelGrid[explorerPos.y][explorerPos.x];
+	// Check key collision
+	if (cellType === 'K') {
+		for (var i = 0; i < keys.length; i++) {
+			var keyPos = getGridPosition(keys[i].x, keys[i].y);
+			if (keyPos && keyPos.x === explorerPos.x && keyPos.y === explorerPos.y) {
+				explorer.collectKey();
+				keys[i].destroy();
+				keys.splice(i, 1);
+				levelGrid[explorerPos.y][explorerPos.x] = ' ';
+				LK.getSound('collect').play();
+				break;
+			}
+		}
+	}
+	// Check door collision
+	if (cellType === 'D') {
+		var door = getDoorAt(explorerPos.x, explorerPos.y);
+		if (door && door.isLocked && explorer.hasKey) {
+			door.unlock();
+			explorer.useKey();
+			keysTxt.setText('Keys: ' + storage.collectedKeys);
+		}
+	}
+	// Check treasure collision
+	if (cellType === 'T') {
+		for (var i = 0; i < treasures.length; i++) {
+			var treasurePos = getGridPosition(treasures[i].x, treasures[i].y);
+			if (treasurePos && treasurePos.x === explorerPos.x && treasurePos.y === explorerPos.y && !treasures[i].isCollected) {
+				treasures[i].collect();
+				break;
+			}
+		}
+	}
+	// Check spike collision
+	for (var i = 0; i < spikes.length; i++) {
+		if (spikes[i].isActive && explorer.intersects(spikes[i])) {
+			explorer.takeDamage();
+			// Move player to a safe position
+			var safeX = explorer.x;
+			var safeY = explorer.y - tileSize;
+			if (isWalkable(Math.floor(safeX / tileSize), Math.floor(safeY / tileSize))) {
+				explorer.x = safeX;
+				explorer.y = safeY;
+			}
+		}
+	}
+	// Check falling rock collision
+	for (var i = 0; i < fallingRocks.length; i++) {
+		var rock = fallingRocks[i];
+		// Trigger rock if explorer is underneath
+		var rockPos = getGridPosition(rock.x, rock.y);
+		if (rockPos && explorerPos.x === rockPos.x && explorerPos.y > rockPos.y && !rock.isTriggered && !rock.isFalling) {
+			rock.trigger();
+		}
+		// Check if rock hits explorer
+		if (rock.isFalling && explorer.intersects(rock)) {
+			explorer.takeDamage();
+			rock.reset();
+		}
+	}
+	// Check river collision (player falls in if there's no bridge)
+	for (var i = 0; i < rivers.length; i++) {
+		var river = rivers[i];
+		var riverPos = getGridPosition(river.x, river.y);
+		if (riverPos && explorerPos.x === riverPos.x && explorerPos.y === riverPos.y && !river.hasBridge) {
+			explorer.takeDamage();
+			// Move player to a safe position
+			var safeX = explorer.x;
+			var safeY = explorer.y - tileSize;
+			if (isWalkable(Math.floor(safeX / tileSize), Math.floor(safeY / tileSize))) {
+				explorer.x = safeX;
+				explorer.y = safeY;
+			}
+		}
+	}
+}
+function moveExplorer(targetX, targetY) {
+	if (!explorer || explorer.isMoving) {
+		return;
+	}
+	var currentGridPos = getGridPosition(explorer.x, explorer.y);
+	var targetGridPos = getGridPosition(targetX, targetY);
+	if (!currentGridPos || !targetGridPos) {
+		return;
+	}
+	// Only allow movement to adjacent cells
+	var dx = Math.abs(targetGridPos.x - currentGridPos.x);
+	var dy = Math.abs(targetGridPos.y - currentGridPos.y);
+	if (dx === 1 && dy === 0 || dx === 0 && dy === 1) {
+		if (isWalkable(targetGridPos.x, targetGridPos.y)) {
+			var cellCenterX = targetGridPos.x * tileSize + tileSize / 2;
+			var cellCenterY = targetGridPos.y * tileSize + tileSize / 2;
+			explorer.moveToward(cellCenterX, cellCenterY);
+		}
+	}
+}
+// Handle touch/mouse events
+function handleGameInput(x, y, obj) {
+	if (!gameStarted) {
+		return;
+	}
+	moveExplorer(x, y);
+}
+// Start game when page loads
+initializeGame();
+// Handle touch/mouse events
+game.down = handleGameInput;
+// Game update loop
+game.update = function () {
+	if (!gameStarted) {
+		return;
+	}
+	// Update UI
+	updateUI();
+	// Check collisions
+	checkCollisions();
+	// Add bridge to first river after collecting all keys (for level 4)
+	if (storage.level >= 4 && storage.collectedKeys >= 1) {
+		for (var i = 0; i < rivers.length; i++) {
+			if (!rivers[i].hasBridge) {
+				rivers[i].addBridge();
+				break;
+			}
+		}
+	}
+};
\ No newline at end of file