from collections import deque
from scipy.spatial import distance

def nishin(x):
    x = format(x, '030b')
    x = list(map(int,str(x)))
    return x

n = int(input())
start, end = map(int,input().split())
start = nishin(start)
end = nishin(end)
stone = list(map(int,input().split()))
stone.sort()
stone = list(map(nishin,stone))

queue = deque()
queue.append(start)


if distance.hamming(start, end) * 30 <= 1:
    print(0)
    exit()

cnt = 1
vv = stone[0]

while queue:
    v = queue.popleft()

    for i in stone:
        if distance.hamming(v, i) * 30 <= 1:
            if distance.hamming(i, end) * 30 <= 1:
                print(cnt)
                exit()

            queue.append(i)

    if int(''.join(map(str, v))) <= int(''.join(map(str, vv))):
        cnt += 1
        
    vv = v

print(-1)