var speed = 20;

$(document).ready(function(){
	$(document).scroll(function(){
		scrollBackground($(window).scrollTop());
	});
	
	$('#sidebar ul li:last-child').css({'background-image' : 'none'});
	$('div.post:last-child').css({'background-image' : 'none'});
	
});

function scrollBackground(newpos){
	$('body').css({'background-position': 'center -'+newpos/speed+'px'});
}