p2 = [1]
while p2[-1] * 2 <= 10 ** 9:
    p2.append(p2[-1] * 2)
N = int(input())
st, en = map(int, input().split())
S = [st] + list(map(int, input().split())) + [en]

dic = {S[i]: i for i in range(N + 2)}
adj = [[] for i in range(N + 2)]
for i in range(N + 2):
    for j in range(len(p2)):
        if S[i] ^ p2[j] in dic.keys():
            adj[i].append(dic[S[i] ^ p2[j]])
        if S[i] ^ p2[j] in dic.keys():
            adj[i].append(dic[S[i] ^ p2[j]])

from collections import deque
qu = deque([0])
dist = [-1] * (N + 2)
dist[0] = 0
while len(qu):
    v = qu.popleft()
    for nv in adj[v]:
        if dist[nv] == -1:
            dist[nv] = dist[v] + 1
            qu.append(nv)
print(max(-1, dist[-1] - 1))