A ray of light falls normally (as shown) on a right angled prism whose  $\mu =\sqrt{1.5}$ and 45°. After passing through prism, it falls on a concave mirror which is at a distance of 27.46cm from the point of emergence of prism. The net deviation of the ray is  $n\times 90°$, (if focal length of the mirror is 10cm) then value of n is