JS continuously scrolls up the effect code

 
<div id=demo style=overflow:hidden;height:139;width:232;background:#f4f4f4;color:#ffffff><div id=demo1><img src="http://www.lanrentuku.com/down/js/images/12460764740.jpg"><img src="http://www.lanrentuku.com/down/js/images/12460764741.jpg"><img src="http://www.lanrentuku.com/down/js/images/12460764742.jpg"><img src="http://www.lanrentuku.com/down/js/images/12460764743.jpg"><img src="http://www.lanrentuku.com/down/js/images/12460764744.jpg"></div> 
<div id=demo2></div> 
</div> 
<script> 
var speed=50 
demo2.innerHTML=demo1.innerHTML 
function Marquee(){ 
if(demo2.offsetTop-demo.scrollTop<=0) 
demo.scrollTop-=demo1.offsetHeight 
else{ 
demo.scrollTop++ 
} 
} 
var MyMar=setInterval(Marquee,speed) 
demo.onmouseover=function() {clearInterval(MyMar)} 
demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)} 
</script> 
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