subtracting columns one at a time?

I want to subtract a number from one column of numbers and I want to see the numbers in that column decrease by the amount taken away. That is the easy part. Once all the numbers are depleted in the 1st column, or the number in the 1st column is not large enough to produce a positive number, I want to reduce the numbers in column 1 to 0 and then start subtracting numbers from the 2nd column, and again reduce the numbers in the 2nd column by the number taken away.

This will be used as a calculator so I would like to be able to use the same formula the full length of the column.

Example

ACB | Current Value | Withdrawal

4 | 5 | 2
4 | 3 | 2
4 | 1 | 2
3 | 0 | 2
1 | 0 | 2
0 | 0 | 1

Thank you