function nahrej()
{
   var url,cislo;
   cislo=document.form1.cat.selectedIndex;
   if (cislo!=-1){
     url=document.form1.cat.options[cislo].value;
     url="http://online.unitconverterpro.com/unit-conversion/convert-alpha/convert.php?cat="+url;
     location.href=url;}
}