Which of the following boxes is placed exactly in the middle?

Study the following information carefully and answer the question given below: Nine boxes named M, N, O, P, Q, R, S, T and U are placed one above other but not necessarily in the same order. Only five boxes are placed between M and O. Q is placed immediate above O. Only three boxes are placed between Q and P. Number of boxes placed between M and P is same as between N and Q. R is placed below N, but not at bottom. Not less than four boxes are placed between Q and R. One box is placed between R and S. Box U is placed above box T.