Series Solutions · Easy problem

With $y = \sum_{n=0}^{\infty} a_n x^n$, the second derivative $\sum_{n=2}^{\infty} n(n-1)a_n x^{n-2}$ is rewritten after an index shift as $\sum_{k=0}^{\infty} c_k x^k$. If $a_5 = 2$, find $c_3$.