Potřebuji sečíst hodnoty na checkboxech, JS znám minimálně,

<form enctype="multipart/form-data" name="formular">


<h2>Sečti to</h2>


<input type="checkbox" value="1" data-cena1="10" name="sluzba" onchange="calc()">1

<input type="checkbox" value="2" data-cena2="11" name="sluzba" onchange="calc()">2

<input type="checkbox" value="3" data-cena3="12" name="sluzba" onchange="calc()">3

<input type="checkbox" value="4" data-cena4="13" name="sluzba" onchange="calc()">4

<input type="checkbox" value="5" data-cena5="14" name="sluzba" onchange="calc()">5
 


<h2>Celkem</h2>  <input type="text" name="celkem" disabled="">
</form>


<script>


function getCheckedCena(radio) 
{
  
for (i = 0; i < radio.length; i++) 
{
    if (radio[i].checked) {
       

return parseInt(radio[i].getAttribute('data-cena'));
    

}
  }
  return 0;
}


function calc()
{
  
document.formular.celkem.value=getCheckedCena1+Cena2+Cena3+Cena4+Cena5(document.formular.sluzba);
}