/* smooth scroll */
function fBacktoTop() {
  var d=document;
  var scroll_left=d.body.scrollLeft || d.documentElement.scrollLeft || d.scrollX || 0;
  var scroll_top=d.body.scrollTop || d.documentElement.scrollTop || d.scrollY || 0;

  // scroll
  if(scroll_top > 500)
  {
    // fast
    scrollTo(scroll_left/2, 500);
    var f=setTimeout("fBacktoTop()", 10);
  }
  else if(scroll_left>0 || scroll_top>0)
  {
    // slow
    scrollTo(scroll_left/2, scroll_top/2);
    var f=setTimeout("fBacktoTop()", 50);
  }else{
      clearTimeout(f);
  }
}