import sys
input = sys.stdin.readline

from collections import deque
N=int(input())
start,end=map(int,input().split())
S=list(map(int,input().split()))
S.append(end)
S.append(start)
SET=set(S)

DP=dict()
DP[start]=0
Q=deque([start])

while Q:
    x=Q.popleft()

    for i in range(32):
        y=x^(1<<i)
        if y in SET:
            if not(y in DP):
                DP[y]=DP[x]+1
                Q.append(y)

if end in DP:
    print(DP[end]-1)
else:
    print(-1)