$(document).ready(function(){
	var winY = $(window).height();
	var wrapper = $('#wrapper');
	var main = $('#content_main');
	var footer = $('#footer');
	var footY = footer.height();
	var header = $('#header');
	var headY = header.height();
	main.css({'min-height':(winY-footY-headY-50)+'px'});
});