window.onload = function(){

	var links = document.getElementById('left');
	var midden = document.getElementById('mid');
	var rechts = document.getElementById('right');

	var linksHoog = links.offsetHeight;
	var rechtsHoog = rechts.offsetHeight;
	var middenHoog = midden.offsetHeight;

	links.style.height=middenHoog+"px";
	rechts.style.height=middenHoog+"px";
	
	

	var content = document.getElementById('content');
	var boxleft = document.getElementById('boxleft');
						
	var contentHoog = content.offsetHeight;
	var boxleftHoog = boxleft.offsetHeight;
	
	contentHoog > boxleftHoog ? boxleft.style.height=contentHoog+"px" : content.style.height=boxleftHoog+-30+"px";
	}