var id=function(o){return document.getElementById(o)}
var scroll=function (o){
	var space=id(o).offsetTop;
	id(o).style.top=space+'px';
	void function(){
		var goTo = 0;
		var roll=setInterval(function(){
			var height =document.documentElement.scrollTop+document.body.scrollTop+space;
			var top = parseInt(id(o).style.top);
			if(height!= top){
				goTo = height-parseInt((height - top)*0.9);
				if (goTo < 30){
					goTo = 0;
				} else if (goTo > 490){
					goTo = 490;
				} else {
					goTo = goTo - 30;
				}
				id(o).style.top=goTo+'px';
			}			
		},50);
	}()
}