window.onload = function () {
   var changetime=4*60;
    var sub_num = 16; 
    setInterval(function () {
        var u = document.getElementById("u_list");
        var list=u.getElementsByTagName("li");
	var first_l=u.removeChild(list[0]);
	u.appendChild(first_l);
    }, changetime*1000);
}