Finding value of definite integral - $f(f(x)) = x$

Question

Question:

If $f(x)$ is such a function so that $f(f(x)) = x$ and $f(0) = 1$ then find the value of: $$ \int_0^1(x+f(x))^{2016}dx$$

I have no clue where to start this question. A small hint would be appreciated.