$(window).load(function() {
   var $sidebar = $("#sidebar"),
   $window = $(window),
   offset = $sidebar.offset(),
   topPadding = 0;
   $window.scroll(function() {
      if ($window.scrollTop() > offset.top && $window.scrollTop() + 626 < $(document).height() - 450) {
         $sidebar.stop().animate({
            marginTop: $window.scrollTop() - offset.top + topPadding
         });
      } else if($window.scrollTop() + 626 >= $(document).height() - 450) {

      }  else {
         $sidebar.stop().animate({
            marginTop: 0
         });
      }
   });
});

function backToTop() {
     var x1 = x2 = x3 = 0;
     var y1 = y2 = y3 = 0;

     if (document.documentElement) {
         x1 = document.documentElement.scrollLeft || 0;
         y1 = document.documentElement.scrollTop || 0;
     }

     if (document.body) {
         x2 = document.body.scrollLeft || 0;
         y2 = document.body.scrollTop || 0;
     }

     x3 = window.scrollX || 0;
     y3 = window.scrollY || 0;

     var x = Math.max(x1, Math.max(x2, x3));
     var y = Math.max(y1, Math.max(y2, y3));

     window.scrollTo(Math.floor(x / 1.3), Math.floor(y / 1.3));

     if (x > 0 || y > 0) {
         window.setTimeout("backToTop()", 25);
     }
 }