Two plane mirrors are placed parallel to each other at a distance $4d$ as shown in the figure. The point source of light S is having wavelength equal to $\mathrm{\lambda }$ . The light is reaching the screen (right of the source) only after reflection. For point $\mathrm{P}$ to be 2nd maxima, the value of $\frac{\mathrm{\lambda }}{2}=\frac{\mathrm{K}{\mathrm{d}}^2}{\mathrm{D}}$ . Where $\mathrm{K}$ is an integer. Find value of $\mathrm{K}$? (assume $\mathrm{ }\mathrm{D}\gg \mathrm{d}$ and $\mathrm{d}\gg \mathrm{\lambda }$)