25.
M, N, O, S, T and U 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. T lives on the topmost floor. Only three people live between T and N. O lives on a floor below N. S lives on an even numbered floor. U lives on an odd numbered floor but not on floor number 5. How many people live between M and N?