from collections import deque

n = int(input())
s, e = map(int, input().split())
stone = set(map(int, input().split()))
stone.add(e)
dist = {s:0}
queue = deque()
queue.append(s)
while queue:
    pos = queue.popleft()
    for i in range(30):
        npos = pos ^ (1 << i)
        if npos not in dist and npos in stone:
            dist[npos] = dist[pos] + 1
            queue.append(npos)

print(dist.get(e, 0) - 1)