General Studies · Puzzles

Seven boxes M, N, O, P, Q, R and S are kept one over the other but not necessarily in the same order. Box R is kept at the fourth position from the bottom. Only one box is kept between R and S. Box M is kept immediately above S. Only two boxes are kept between M and N. Box O is kept at some position above P, and Box Q is kept at some position below P. How many boxes are kept between N and S?