function btt_install( ) {
 if( !document.getElementsByTagName ) { return; }
 var a, i = 0;
 while(( a = document.getElementsByTagName( 'a' )[i++] )) {
  if( '#top' == a.getAttribute( 'href' )) {
   a.onclick = function() { backToTop(); return false; }
  }
 }
}

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);
    }
    return false;
}