#yuki1576
from collections import deque
n=int(input())
s,e=map(int,input().split())
st=list(map(int,input().split()))
dist={x:-1 for x in st}
dist[s]=0
dist[e]=-1
d=deque()
d.append(s)
while d:
 v=d.popleft()
 for x in range(30):
  i=v^(2**x)
  if i not in dist:
   continue
  if dist[i]!=-1:
   continue
  dist[i]=dist[v]+1
  d.append(i)
if dist[e]==-1:
 print(-1)
else:
 print(dist[e]-1)