function setCookie(name, value){
var curCookie = name+"="+escape(value)
document.cookie = curCookie
}
function getCookie(name){
var prefix = name + "="
var cookieStartIndex = document.cookie.indexOf(prefix)
if(cookieStartIndex == -1) return null
var cookieEndIndex = document.cookie.indexOf(";",cookieStartIndex+prefix.length)
if (cookieEndIndex == -1)
	cookieEndIndex = document.cookie.length
return unescape(document.cookie.substring(cookieStartIndex+prefix.length,cookieEndIndex))
}

function preLoad(n){
var img=new Array();
var i=new Number();
	for(i=0;i<n;i++){
		img[i]=new Image()
		img[i].src="images/acs-trees"+(i+1)+".jpg"
	}
}
function setBgImg(n){
var inc=getCookie("bg");
	if (inc==null){
		inc=Math.floor(Math.random()*(n-1))+1
		if (document.all||document.getElementById)
			window.onload=new Function("preLoad("+n+")");
	}
	else
		if (inc>n) inc=1;
	document.write('<style type="text/css">#lmasthead{background-image:url("images/acs-trees'+inc+'.jpg");</style>');
	setCookie("bg",++inc);
}
setBgImg(6);