NL-BXMO-TST 2017 Problem 2

Let define a function $f: \mathbb{N} \rightarrow \mathbb{Z}$ such that : $i)$ $f(p)=1$ for all prime numbers $p$ . $ii)$ $f(xy)=xf(y)+yf(x)$ for all positive integers $x,y$ find the smallest $n \geq 2016$ such that $f(n)=n$