In 2019 Roni Edwin solved the following problem in the IMO representing his home country of Ghana. Is he smarter than you?

Let $\mathbb{Z}$ be the set of integers. Determine all functions $f : \mathbb{Z} \rightarrow \mathbb{Z}$ such that, for all integers a and b, $f (2a) + 2f (b) = f (f (a + b))$.