A line charge of length $\frac{\mathrm{a}}{2}$ is kept at the center of an edge BC of a cube ABCDEFGH having edge length ' $a$ ' as shown in the figure. If the density of line charge is $\lambda \mathrm{C}$ per unit length, then the total electric flux through all the faces of the cube will be $\_\_\_\_$ . (Take, $\epsilon_0$ as the free space permittivity)