Seven persons, P, Q, R, S, T, U and V, live in a building, which has seven floors. The floor, which is at the bottommost position is numbered as 1, the floor above it is numbered as 2 and so on. P lives on an even numbered floor. There are two floors between P and T. Q lives immediately below T. Q does not live on a prime numbered floor. V lives three floors above R. V does not live on a prime numbered floor. S lives above U.  How many persons live between S and U?