/* -*- coding: utf-8 -*-
 *
 * 1577.cc:  No.1577 織姫と彦星2 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 50000 + 2;
const int BN = 30;

/* typedef */

typedef queue<int> qi;
typedef map<int,int> mii;

/* global variables */

int sts[MAX_N], ds[MAX_N];
mii vmap;

/* subroutines */

inline int bitcnt(int bits) {
  int cnt = 0;
  for (; bits > 0; bits >>= 1)
    if (bits & 1) cnt++;
  return cnt;
}

/* main */

int main() {
  int n;
  scanf("%d%d%d", &n, sts, sts + 1);

  n += 2;
  for (int i = 2; i < n; i++) scanf("%d", sts + i);

  for (int i = 0; i < n; i++) vmap[sts[i]] = i;

  memset(ds, -1, sizeof(ds));
  ds[0] = 0;

  qi q;
  q.push(0);

  while (! q.empty()) {
    int u = q.front(); q.pop();
    if (u == 1) break;

    for (int i = 0, bi = 1; i < n; i++, bi <<= 1) {
      mii::iterator mit = vmap.find(sts[u] ^ bi);
      if (mit != vmap.end()) {
	int v = mit->second;
	if (ds[v] < 0) {
	  ds[v] = ds[u] + 1;
	  q.push(v);
	}
      }
    }
  }

  printf("%d\n", (ds[1] < 0) ? -1 : ds[1] - 1);
  return 0;
}