Determine the last "value" in a column of formulas

Good afternoon again,

I have 3 columns, A, B, & C.
Columns A & B have input values. Column C is a calculation.
I need to determine the last "Value" displayed in Column C.

A | B | C
1 | 2 | -1
3 | 0 | 2
1 | 1 | 2
2 | 1 | 3
1 | 2 | 2
0 | 2 | 0
0 | 3 | -3

As mentioned, A & B are data entry values.
Cell C1 is calculated with IF(A1="","",(A1-B1))
From Cell C2 onwards, the formula is IF(A2="","",(A2-B2+A1))

In a different cell (say F1) I would like to display the last displayed value, that is in this case -3.
The range of data would be A1:C25 - but cells A8:B25 are empty (for now), and obviously [because of the IF(A?="","") string] cells C8:C25 "appear" blank, but contain a formula.

Thanks for any assistance.
HGL