function open_small_window(strona,szer,wys){
   var w = 480, h = 340;
 
   if (document.all) {
     w = document.body.clientWidth;
     h = document.body.clientHeight;
   }
   else if (document.layers) {
     w = window.innerWidth;
     h = window.innerHeight;
   }
 
   if(screen.width>0){
    w= screen.width;
    h= screen.height;
   }
   
   var popW = szer, popH = wys;
   var leftPos = (w-popW)/2, topPos = (h-popH)/2;
   var parametres = "width="+popW+",height="+popH+",top="+topPos+",left="+leftPos;
   
   window.open(strona,"ContactUs",parametres);
  }