In Jollybee Chess Championship 2008, there are a number of players who have withdrawn themselves from the championship of 64 players (in this problem, we generalized it into 2^N

players). Due to the nature of the competition, which is a regular knock-out tournament, and also the short notice of the withdrawals, some matches had been walkover matches (also known as a w/o, a victory due to the absent of the opponent).

If both players are available then there will be a normal match, one of them will advance to the next phase. If only one player is available then there will be a walkover match, and he/she will automatically advance. If no player is available then there will be no match.

In the left figure, the player #3 and #4 are withdrawn from the tournament, leaving a total of one w/o match (at match #3).

Given the list of players who withdraw right before the tournament start, calculate how many w/o matches to happen in the whole tournament, assuming that all of the remaining players play until the end of the tournament (winning or knocked-out).