How to include exceptions and conditions in your formula such as IF/THEN, AND/OR, etc

I have a large range of data, and I need the cells in one column to calculate the sum of several cells UNLESS another paticular cell has a value greater than 0, then the value in that the corresponding cell in that column should equal that cell.

For example:

Q2 = A2+B2+C2+D2 UNLESS E2>0 THEN Q2 = E2

Does anyone what formula I need to do this?

Thanks!