quote = new Array();
quote[0]="1"; 
quote[1]="2"; 
quote[2]="3"; 
var date = new Date();
var sec = date.getSeconds();
var index = (sec % quote.length);
var topbanner = document.getElementById("topbanner");
var x = topbanner.className.match(/banner topbg([0-9]+)/)[1];
topbanner.className = topbanner.className.replace("banner topbg" + x,"banner topbg" + quote[index]);