def checkhamming(n, m):
    return bin(n ^ m).count('1')


N = int(input())
start, end = map(int, input().split())
stones = list(map(int, input().split()))
stones.append(end)

q = [[start, 0]]

while len(q):
    # print(q)
    now, count = q.pop(0)
    if count > len(stones)+1:
        break
    # print(now, count)
    for stone in stones:
        if checkhamming(now, stone) <= 1 and now != stone:
            if stone == end:
                print(count)
                exit()
            else:
                q.append([stone, count+1])
    
print(-1)