function MenuZobrazPrvni(id)
{
  var lis = document.getElementById('menu_ul_prvni').getElementsByTagName("LI");
 
  for (var i=0; i<lis.length; i++) 
  {
    lis[i].className = lis[i].className.replace(new RegExp("on\\b"), "");
  }
  
  document.getElementById('prvni_' + id).className += ' on';
  
  var class_name = document.getElementById('menu');
  if (class_name != null) class_name.className          = 'aktivni_' + id;
  
  class_name = document.getElementById('menu_homepage');
  if (class_name != null) class_name.className          = 'aktivni_' + id;
}

function MenuZobrazDruha(id)
{
  //MenuSkryjDruha();
  
  document.getElementById('druha_' + id).className += ' on';
}

function MenuSkryjDruha(id)
{
  document.getElementById('druha_' + id).className = document.getElementById('druha_' + id).className.replace(new RegExp("on\\b"), "");
}