var W = screen.width;
if (W == 800) document.body.background = "bg/800.jpg";
else if (W == 1024) document.body.background = "bg/1024.jpg";
else if (W == 1280) document.body.background = "bg/1280.jpg";
else if (W == 1360) document.body.background = "bg/1360.jpg";
else if (W == 1440) document.body.background = "bg/1440.jpg";
else if (W == 1600) document.body.background = "bg/1600.jpg";
else if (W == 1680) document.body.background = "bg/1680.jpg";
else document.body.background = "bg/1600.jpg";