# Yay for... 2015?

**Algebra**Level 5

Find the number of functions \(f\) that map non-negative integers to non-negative integers such that

\[f(f(x)) = x + 2015.\]

**Notes:**

By *map non-negative integers to non-negative integers*, we mean that the domain and range of \(f\) are both the set of non-negative integers.