function random(){

		var img;	
	
		var n1 = Math.random()*4;

		var n2 = Math.round(n1); 

		if (n2 == 0) img = 'images/600x120_1.jpg';	
		else if (n2 == 1) img = 'images/600x120_2.jpg';
		else if (n2 == 2) img = 'images/600x120_3.jpg';
	        else img = 'images/600x120_4.jpg';	
		
		return img;
	}