function sortNum(a,b) { return b-a} 
function fix_height(one,two,three) {
if (document.getElementById(one)) {
var obj=new Array(3);
var option=[one,two,three];
for(var i=0; i<option.length; i++) {
document.getElementById(option[i]).style.height="auto";
obj[i]=document.getElementById(option[i]).offsetHeight;
nh=obj.sort(sortNum);
} 
nh1=nh.splice(1,2);
for(var i=0; i<option.length; i++) {
document.getElementById(option[i]).style.height=nh+"px";
}
}
}

window.onload=function(){
fix_height('left_menu','second_6','third_6');
}