I am trying to study probability theory by myself. I asked myself a question about expectation, and I have no idea how to solve it. Please help me with solution and my understanding. The question I asked is following: Let $a, b, c, d$ be non-negative natural numbers, say from the set $\{0, 1, ..., n\}.$ Calculate the expectation $ E\left( (-1)^{a+b+c+d}\right). $
Thank you for your help.