function getanImage()
{
    var ranNum= Math.floor(Math.random()*4);

    var top = new Array(4)
     top[0]= "images/rs1.jpg";
     top[1]= "images/rs2.jpg";
     top[2]= "images/rs3.jpg"; 
     top[3]= "images/rs4.jpg";
  
  
	document.top_img.src = top[ranNum]; 
	    
   }