var current = 1;
var timer = 4000;
var fade = 1000;

function SwitchPromo() {

	var previous = (current + 2) % 3;
	
	$("#promo" + previous).fadeOut(fade, function() {
		$("#promo" + previous).hide();
		
		$("#promo" + current).fadeIn(fade, function() {
			current += 1 
			current %= 3;
			setTimeout(SwitchPromo, timer);
		});
	});

}

$(document).ready(function() {
	setTimeout(SwitchPromo, timer);
});