N = int(input())
start ,end = map(int,input().split())
stone = set(list(map(int,input().split())))

s = set()
from collections import deque
import sys
q = deque()
q.append((start,0))
s.add(start)

m = max(stone)
k = 1
while 1 << k <= m:
    k += 1
while len(q):
    now,d = q.popleft()
    for j in range(k):
        next = now ^ (1 << j)
        if next == end:
            print(d)
            exit()
        if next in stone and next not in s:
            s.add(next)
            q.append((next,d + 1))
print(-1)