var currentIndex = -1

var backgrounds = ["url('images/programs1.jpg')",
	"url('images/programs2.jpg')",
	"url('images/programs3.jpg')",
	"url('images/programs4.jpg')"];

function changeBackground() {

	currentIndex = (currentIndex + 1) % backgrounds.length;
	document.getElementById('contents').style.background = backgrounds[currentIndex] + " no-repeat center center";
	setTimeout('changeBackground()', 5000);

}