js無縫滾動，現要求：滾動條數少於3條，則停止滾動。超過三條，便自動滾動。請大神幫忙解決壹下

<div style="height:6000000px;">

<div id="scroll_begin" style="float:left;" >

<div class="ks_pic_img"><img src='/uploads/1.jpg' border='0' width='126'height='160' ></div>

<div class="ks_pic_img"><img src='/uploads/1.jpg' border='0' width='126'height='160' ></div>

<div class="ks_pic_img"><img src='/uploads/1.jpg' border='0' width='126'height='160' ></div>

<div class="ks_pic_img"><img src='/uploads/1.jpg' border='0' width='126'height='160' ></div>

</div>

<div id="scroll_end" style="float:left;" ></div></div>

</div>

<script>

function ScrollImgLeft(){

var speed=20,

doc=document,

scroll_begin = doc.getElementById("scroll_begin"),

scroll_end = doc.getElementById("scroll_end"),

scroll_div = doc.getElementById("scroll_div");

scroll_end.innerHTML=scroll_begin.innerHTML;

function Marquee(){

if(scroll_end.offsetHeight-scroll_div.scrollTop<=0)

scroll_div.scrollTop-=scroll_begin.offsetHeight

else

scroll_div.scrollTop++

}

var MyMar=setInterval(Marquee,speed)

scroll_div.onmouseover=function() {clearInterval(MyMar)}

scroll_div.onmouseout=function() {MyMar=setInterval(Marquee,speed)}

}

ScrollImgLeft();

</script>