Ar Bs Ec Ar Bs Ec
20 36 14 10 7

I am trying to sum the above columns. Column 1-3 supercede columns 4-6, in
the sense that if column 4 has a figure in there and so does column 1, it is
column 1s figure that needs to be included in the total not column 4. So for
the above example i would need the formula to work out 20+36+7=63.

How would i do this?