function change_background()
{
   var main_left_div=document.getElementById("main_left_div");
   var main_center=document.getElementById("main_center");
   
   var mLeftHeight=main_left_div.offsetHeight;
   var mCenterHeight=main_center.offsetHeight;
   
   if(mCenterHeight>mLeftHeight)
   {
	  
	   main_left_div.style.height=mCenterHeight+"px";
	   }
   
	}