var layerCount;
var currentLayer;
function countLayers(){
		var i=0;
		var layerExists=true;
		while (layerExists)
		{
		layerToCheck='banner'+i;
		if (document.getElementById(layerToCheck)) 
		  {
		  i++;
		  } else {
		  layerExists=false;
		  }
		}
		layerCount=i;
		no=Math.random()*layerCount;
		no=Math.floor(no);
	  firstLayerToShow='banner'+no;
		document.getElementById(firstLayerToShow).style.display = "block";
		currentLayer =no;
		var t=setTimeout("rotateBanners()",15000)
}

function rotateBanners(){
		layertohide='banner'+currentLayer;
		document.getElementById(layertohide).style.display = "none";
		currentLayer++;
		if (currentLayer==layerCount) {
		  currentLayer=0;
		}
		var newLayer='banner'+currentLayer;
		document.getElementById(newLayer).style.display = "block";
		var t=setTimeout("rotateBanners()",15000)
}