import random
import queue
def solve(start, end, stones):
    stone_set = set(stones)
    checked_set = set()
    que = queue.Queue()
    que.put((start, 0))
    while not que.empty():
        current, distance = que.get()
        next_distance = distance + 1
        for i in range(31):
            candidate = current ^ (1<<i)
            if candidate == end:
                return next_distance - 1
            
            if candidate in stone_set and candidate not in checked_set:
                checked_set.add(candidate)
                que.put((candidate, next_distance))
    return -1

if __name__ == '__main__':
    N = int(input())
    start, end = list(map(int, input().split()))
    stones = list(map(int, input().split()))
    print(solve(start, end, stones))