n,S,G,*a, = map(int,open(0).read().split())
a = list(set(a)) + [S,G]
za = {ai:i for i,ai in enumerate(a)}
n = len(a)

g = [[] for _ in range(n)]
for i,ai in enumerate(a):
    for j in range(32):
        v = ai^(1<<j)
        if v in za:
            g[i].append(za[v])

d = [-1]*n
q = [n-2]
d[n-2] = 0
for v in q:
    for i in g[v]:
        if d[i] == -1:
            d[i] = d[v] + 1
            q.append(i)
print(max(-1,d[-1]-1))