Z Tower stands near the city of XYJ. We require: a person who has been on top of the tower 5 minutes, must go down; while it's coming down, people
those at the bottom of the tower must wait. Climbing the stairs of the tower and descending
the stairs of the tower take one minute each. Every moment on the stairs
there can only be one person.
Now there is no one at the top of the tower, at the foot of the tower there is a person in line.
After T minutes, B more people will come. After what time (minutes) all people
come out of the tower (the last person to go down the stairs)