function prepocti(form, kDispozici){
  ceny = new Array (250, 230, 120, 120);  sleva12 = 90;
          
  cena = 0;
  if(document.forms[form].nab1next.checked)
    cena += ceny[0];
  if(document.forms[form].nab2next.checked)
    cena += ceny[1];
  if(document.forms[form].nab3next.checked)
    cena += ceny[2];
            
  if(document.forms[form].nab1next.checked && document.forms[form].nab2next.checked)
    cena -= sleva12;

  document.forms[form].celkem.value = cena+" Kč";
  if((kDispozici - cena) < 0)
    document.forms[form].celkem.style.color = '#880000';
  else
    document.forms[form].celkem.style.color = '#000000';
}