A beam of light consisting of two wavelengths $7000~\mathop A\limits^o $ and $5500~\mathop A\limits^o $ is used to obtain interference pattern in Young's double slit experiment. The distance between the slits is $2.5 \mathrm{~mm}$ and the distance between the plane of slits and the screen is $150 \mathrm{~cm}$. The least distance from the central fringe, where the bright fringes due to both the wavelengths coincide, is $n \times 10^{-5} \mathrm{~m}$. The value of $n$ is __________.