import sys

N = int(input())
start,end = map(int,input().split())
S = list(map(int,input().split()))
S = [start] + S + [end]
E = [[] for _ in range(N+2)]
A = [pow(2,i) for i in range(30)]
A.append(0)
A = set(A)

for i in range(N+1):
    for j in range(i+1,N+2):
        if S[i] ^ S[j] in A:
            E[i].append(j)
            E[j].append(i)

visited = [0] * (N+2)
que1 = {0}
que2 = set()
visited[0] = 1
cnt = 0
while que1:
    for q in que1:
        if q == N+1:
            print(cnt-1)
            sys.exit()
        for e in E[q]:
            if visited[e] != 1:
                visited[e] = 1
                que2.add(e)
    que1,que2 = que2,que1
    que2.clear()
    cnt += 1
print(-1)