function alignHeight($elementA,$elementB){
	var heightA = $elementA.height();
	var heightB = $elementB.height();
	var heightPublic = heightA<heightB?heightB:heightA;
	$elementA.css({height:heightPublic+'px'});
	$elementB.css({height:heightPublic+'px'});
}
window.onload = function(){alignHeight($('#sider'),$('#cont'))}