function getWindowHeight() {
			var windowHeight = 0;
			if (typeof(window.innerHeight) == 'number') {
				windowHeight = window.innerHeight;
			}
			else {
				if (document.documentElement && document.documentElement.clientHeight) {
					windowHeight = document.documentElement.clientHeight;
				}
				else {
					if (document.body && document.body.clientHeight) {
						windowHeight = document.body.clientHeight;
					}
				}
			}
			return windowHeight;
		}
		function setFooter() {
			if (document.getElementById) {
				var windowHeight = getWindowHeight();
				if (windowHeight > 0) {
					var headerHeight = document.getElementById('header').offsetHeight;
					var footerHeight = document.getElementById('footer').offsetHeight;
					var mainElement = document.getElementById('main');
					var difff = (windowHeight - (footerHeight + headerHeight + 22)); //to 20 einai to padding tou #main
					mainElement.style.height = difff + 'px';						 //to 2 einai to panw-katw border tou whole
				}
			}
		}
		window.onload = function() {
			setFooter();
		}
		window.onresize = function() {
			setFooter();
		}