var p = 0;
var billen = 1;
 
  function ing_mozgat() 
  {
    if( billen == 1 ) p--;
    if( p == -1500 ) billen=0;
    if( billen == 0 ) p++;
    if( p == 0 ) billen=1; 
        
    document.getElementById("mozog").style.top = p +'px';
    setTimeout("ing_mozgat()", 25);
  }