Compute the surface integral over the given oriented surface:

$\mathbf{F}=y^{3} \mathbf{i}+6 \mathbf{j}-x \mathbf{k},\quad$ portion of the plane $x+y+z=1$ in the octant $x, y, z \ge 0,\quad$ downward-pointing normal

$\iint_S \mathbf{F} \cdot d\mathbf{S} =$