What is the Fourier series expansion for given function?

Question

For the function $f(x)=\left\{\begin{matrix}-2, -\pi < x <0 \\ 2, 0<x<\pi \end{matrix}\right.$

The value of $a_n$ in the Fourier series expansion of f(x) is

1. 2
2. 4
3. 0
4. -2