$(function() {

    var $sidebar   = $("div.followsidebar"),
        $window    = $(window),
        $contentsBox = $("div.entry"),
        offset     = $sidebar.offset(),
        innerHeight = $contentsBox.innerHeight(),
        sidebarHeight = $sidebar.outerHeight(),
        topPadding = 15;

  if($sidebar.length) {
    $window.scroll(function() {
    if($window.scrollTop() - offset.top + sidebarHeight + topPadding < innerHeight - 90){
        if ($window.scrollTop() > offset.top) {
            $sidebar.stop().animate({
                marginTop: $window.scrollTop() - offset.top + topPadding
            });
        } else {
            $sidebar.stop().animate({
                marginTop: 0
            });
        }
    }
    });
  }
});