from collections import deque

def main():
    twos = [1]
    MAX = 35
    for i in range(MAX):
        twos.append(twos[-1]*2)
    twos = set(twos)
    #print(twos)

    N = int(input()); INF = float("inf")
    N += 2
    start,end = map(int,input().split())
    stones = [start] + list(map(int,input().split())) + [end]
    dic = {}
    for i in range(N):
        dic[stones[i]] = i
    G = [[] for _ in range(N)]
    used = set([])
    for stone in stones:
        base = 1
        for i in range(MAX):
            if (stone>>i)&1 == 1:
                adj = stone - base
            else:
                adj = stone + base
            base *= 2
            if adj not in dic: continue
            u = dic[stone]
            v = dic[adj]
            if v < u: #常にu < vの関係
                u,v = v,u
            if (u,v) in used: continue
            G[u].append(v)
            G[v].append(u)
            used.add((u,v))
    #print(G)
    D = [-1]*N
    Q = deque([])
    Q.append(0)
    D[0] = 0
    while Q:
        v = Q.popleft()
        for u in G[v]:
            if D[u] != -1: continue
            D[u] = D[v] + 1
            Q.append(u)
    #print(D,N)
    if D[N-1] == -1:
        print(-1)
    else:
        print(D[N-1] - 1)

if __name__ == '__main__':
    main()