Surface Integrals, Stokes & Divergence · Easy problem

Find the upward flux $\iint_S \mathbf F\cdot d\mathbf S$ of the constant field $\mathbf F = (0, 0, 3)$ through the horizontal disk $S$: $z = 1$, $x^2 + y^2 \le 4$. Give an exact answer in terms of $\pi$.