var image="";
if (screen.width <= 640) {
image="640.jpg";
}
else if (screen.width <= 800) {
image="800.jpg";
}
else if (screen.width <= 1024) {
image="1024.jpg";
}
else if (screen.width <= 1152) {
image="1152.jpg";
}
else if (screen.width <= 1280) {
image="1280.jpg";
}
else {
image="1600.jpg";
}