3. The function $f$ is defined on the set of non-negative integers $\mathbb{N}_{0}=\mathbb{N} \cup\{0\}$, and takes values in the same set $\mathbb{N}_{0}$. For every $n \in \mathbb{N}_{0}$, it holds that $f(f(n))+f(n)=2 n+3$. Find $f(2012)$.