How to fetch and edit multiple subform fields depending on the value of another subform field

Hi,

I have a main form "Add_Company_Details" which has a subform "Add_Bill".

Main Form "Add_Company_Details" contains:

1. Balance (currency field)

2. Subform "Add_Bill":

1. Amount (currency field)

2. Paid1 (Dropdown field with 2 options: "YES" or "NO")

The "Balance" field in the main form calculates the sum of all related "Amount" fields in the subform. I'm using a deluge script (on success) while a record is being created or edited in "Add_Company_Details":

total = 0;
for each r in input.Add_Bill
{
total = total + ifnull(r.Amount,0);
}
input.Balance = total;

So far so good. What I'm trying to achieve now is:

1. If the subform field "Paid1" dropdown is set to "YES" the corresponding subform field "Amount" should be converted into a positive number

2. If the subform field "Paid1" dropdown is set to "NO" the corresponding subform field "Amount" should be converted into a negative number

3. The main form field "Balance" should only sum up "Amount" fields that contain a negative number or where the "Paid1" field is set to "NO".

I've tried multiple "For each" scripts but had no luck so far.

Any help is appreciated.

Thanks