function comprovaRes(primera){
	if (primera){
		if (screen.width < 800){
			location.href="index.php?tam=1";
		}
		else if (screen.width < 1024 && screen.width >= 800){
			location.href="index.php?tam=2";
		}
		else if (screen.width < 1280 && screen.width >= 1024){
			location.href="index.php?tam=3";
		}
		else if (screen.width >= 1280){
			location.href="index.php?tam=4";
		}
	}	
}