function rand(n) {
	return ( Math.floor ( Math.random ( ) * n + 1 ) );
}

function bg_switch() {
	var num = rand(4);
	//var num = 4;
	document.getElementById("content").style.backgroundImage = "url(images/bg" + num +".jpg)";
	//alert(document.getElementById("content").style.backgroundImage);
}