Sum values of multiple cells IF data exists in neighboring cells

Can anyone help me to figure out a cell formula that would accomplish this:

I want cell "G1" to show the sum of the numbers in A1, C1, and E1 IF data exists in B1, D1, and/or F1

So if data only exists in B1 and D1, but F1 is blank, then "this cell" will only show the sum of A1 and C1 (and will not include the number data from E1 in the sum).

This is for a job payment tracking spreadsheet. I will have six sets of two columns:

A1: Payment 1
B1: Payment 1 Paid on (Date)
C1: Payment 2
D1: Payment 2 Paid on (Date)
E1: Payment 3
F1: Payment 3 Paid on (Date)

... and the G1 would be:

G1: Total Amount Paid So Far

When Payment 1 is received from the client, I will enter that day's date in B1... etc.


If anyone has any other methods to do this, I am more than open to suggestions.

Thanks!

In G1, formatted as General:

=(A1*ISNUMBER(B1)) + (C1*ISNUMBER(D1)) + (E1*ISNUMBER(F1))