n = int(input())
start,end = map(int,input().split())
stone = list(map(int,input().split()))
stoneMax = max(stone)
maxLen = int(len(bin(stoneMax)[2:]))

setStone= set(stone)
from collections import deque
def bfs(u):
    queue = deque([u,0])
    while queue:
        v = queue.popleft()
        dis = queue.popleft()
        h = serchHam(v)
        if end in h:
            print(dis)
            exit()
        # stoneS = stone.copy()
        for i in h:
            if i in setStone:
                queue.append(i)
                queue.append(dis+1)
                # stone.remove(i)
    print(-1)
    exit() 
      
def serchHam(a):
    h=[]
    abin = bin(a+2**maxLen)[2:]
    for i in range(1,maxLen+1):
        if abin[i] == '0':
            hh = 2**(maxLen-i)+a
        else:
            hh = a-2**(maxLen-i)
        # if hh in stone:
        h.append(hh)
    # print(h)
    return h

bfs(start)