// function Voltar ao Topo
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);
  }
}