A Young's double slit interference arrangement with slits S1 and S2 is immersed in water (refractive index =4/3) as shown in the figure. The positions of maxima on the surface of water are given by x2=p2m2λ2−d2, where λ is the wavelength of light in air (refractive index =1), 2d is the separation between the slits and m is an integer. The value of p is