Javascript for Acrobat field population in 2 different fields based on negative or positive number

I am working on an income tax form where the sum of a calculation in one field determines which of two fields to list it in.

The calculation of field one should say if the number is a loss it is listed in field 1. If it is a gain, it should list in field 2.

How do I structure that in javascript in Acrobat?

Thanks!