i am now developing a wed-based system involving JS calculation which is ADD operator in form.
but i still can't figure this out

function jumkerusi()
{


var a = parseInt(document.forms[0].jumbyrsofa.value);
var b = parseInt(document.forms[0].jumbyrvip.value);
var c = parseInt(document.forms[0].jumbyrplastik.value);
var s = parseInt(document.forms[0].jumbyrkerusi.value);

s= a+b+c;


document.forms[0].jumbyrkerusi.value =s;
}