Calculate $\displaystyle \iint\limits_S \vec{F} .\vec{n} dS $:

$\displaystyle \vec{F} (x, y, z)$: (x, y, 2z - x - y)

S: y - z = 0 $\displaystyle 0 \leq x \leq 1,$ $\displaystyle 0 \leq z \leq 1$

y + z = 0 $\displaystyle 0 \leq x \leq 1,$ $\displaystyle 0 \leq z \leq 1$

__________________________

The answer is 0 (zero), so i'm wondering if there is a trick to solve this problem.

If not, I know how to aplly the definition to solve it.