function average()
{
   var items = average.arguments.length
   var sum = 0
   for (i = 0; i < items;i++)
   {
      sum += average.arguments[i]
   }
   return (sum/items)
}
function zobraz_skryj(divid){
  if(document.getElementById(divid).style.display == 'block'){
    document.getElementById(divid).style.display = 'none';
  }else{
    document.getElementById(divid).style.display = 'block';
  }       
}