In a cuboid of dimension $2 \mathrm{~L} \times 2 \mathrm{~L} \times \mathrm{L}$, a charge $q$ is placed at the center of the surface '$\mathrm{S}$' having area of $4 \mathrm{~L}^{2}$. The flux through the opposite surface to '$\mathrm{S}$' is given by