Question about NOR gates and overflow

[seang]

How do I develop a minimal NOR circuit that detects overflow by examining the sign bits of two addends (A and B) and their sum (S)?

Doesn't this depend on how long the addends A and B are? Is there anyway I can generalize the result to n bit addends?

or perhaps I can just designate one input as 'the carry in', compare the MSB of the two addends and go from there?

 

[doodle]

I believe the problem requires you to consider only the MSB of A and B, and the sum S of these bits. What are the overflow conditions given these 3 inputs? Work it out from there.