23.
N, R, S, W, X, and Z live on six different floors of the same building. The lowermost floor in the building is numbered 1, the floor above it number 2, and so on till the topmost floor is numbered 6.
N lives on floor number 2. No one lives between N and R. Only three people live between R and S. W lives immediately above X. On which floor number does Z live?