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 / 2), Math.floor(y / 2));

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