PRESENT BY LEVI

Levi has to give presents to children on new year eve. A large stack of n present numbering from 1 to n is present; the topmost present has number x1, the next present is x2, and so on; the bottom present has number xn. All numbers are distinct. He has a list of m distinct presents he has to send: b1, b2, ..., bm. He will send them in the order they appear in the list. In order to give a prese