$(document).ready(function(){
	width = screen.width;
	height = $(window).height();
	if(width <= '1420' && height <= '1024'){$('#site_bg').addClass('site_bg1').css('min-height',height)}
	else if(width <= '1650' && height <= '1200'){$('#site_bg').addClass('site_bg2').css('min-height',height)}
	else{$('#site_bg').addClass('site_bg3').css('min-height',height)}
    $('.wrapper').css('min-height',height-300)
});