A -------------------------------------- C 1 2 3 | | 1 3 2 | | | | | | | B is shown, the station is scheduled vehicle, built a stack type station, such as a vehicle number number 1, 2, 3 from A, using the B-rail result from 1, 3, 2 C out of the station, the conditions cannot go back, that is, can't B-> A, C-> B, C-> A, the question is if there is N car from A, how many outbound mode? ? ?
