window.onload = Laduj;
  
    function Pokaz()
    {
       var ul = document.getElementById('menu');
  
       var elements = ul.getElementsByTagName('li');
  
       for (var i = 0; i < elements.length ; i++ )
       {
          elements[i].style.display = "block";
       }
  
    }
  
    function Ukryj()
    {
       var ul = document.getElementById('menu');
  
       var elements = ul.getElementsByTagName('li');
  
       for (var i = 0; i < elements.length ; i++ )
       {
          elements[i].style.display = "none";
       }
  
    }
  
    function Laduj()
    {
       var li = document.getElementById('main')
       li.onmouseover = Pokaz;
       li.onmouseout = Ukryj;
    }