Avoid Contact

A hostel has $N$ rooms in a straight line. It has to accommodate $X$ people. Unfortunately, out of these $X$ people, $Y$ of them are infected with chickenpox. Due to safety norms, the following precaution must be taken: - No person should occupy a room directly adjacent to a room occupied by a chickenpox-infected person. In particular, two chickenpox-infected people **cannot** occupy adjacent roo