var referrer = GetCookie("referrer");
if ( !referrer || referrer == 'null' )
{
	var expdate = new Date ();
	expdate.setTime (expdate.getTime() + (1800000)); // 30 minutes
	setCookie("referrer", document.referrer, expdate);
}
else
{
	var expdate = new Date ();
	expdate.setTime (expdate.getTime() + (1800000)); // 30 minutes
	DeleteCookie("referrer");
	setCookie("referrer", referrer, expdate);
}