In standard YDSE $(D>>d>>\lambda )$  with identical slits $S_1$  and $S_2$ light reaching a point. A on the screen opposite to slit  $S_2$ has an intensity I. It was also found that when only one of the two slits $S_1$  or  $S_2$ was illuminated by same light beam, the intensity at A is still I. Now when a third slit  $S_3$ of four times the slit width is made as shown  $(S_1{S}_2=S_2{S}_3=d)$ and all the three slits are illuminated then intensity of light reaching A is nI where n = ________