function kkb(){
var jsvyska = document.getElementById('merak').offsetHeight;
var finalt = document.documentElement.offsetHeight;
if (finalt>jsvyska+19+19+38)                              {
  document.getElementById('menu').style.position='fixed';}
else         {
  document.getElementById('menu').style.position='absolute';

  //alert('s');
  }
}

function kk(){
kkb();
setTimeout("kkb()", 100);
}

window.onload = kk;
window.onscroll = kk;
window.onresize = kk;