I am trying to minus the value of "f1" from "f2" it works fine. However i want it just once but when i click the submit more more button it reduces every time the value of f1 from f2. How can it be done only once. It works well when i put value instead of when i call it from script.

```
    <form name=bills>

<p><input type="text" name="f1" size="20">
<input type="text" name="f2" size="20" value="30"></p>
    <input type="button" value="Submit" onclick="cbs(this.form)" name="B1">

    <Script>
    function cbs(form)

    {
        form.f2.value = (([document.bills.f2.value] * 1) - (document.bills.f1.value * 1))
    }

```

pls help