#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  constexpr int B = 30;
  int n; cin >> n;
  vector<int> stone(n + 2);
  cin >> stone.front() >> stone.back();
  FOR(i, 1, n + 1) cin >> stone[i];
  map<int, int> m;
  REP(i, n + 2) m[stone[i]] = i;
  vector<int> dist(n + 2, -1);
  dist[0] = 0;
  queue<int> que({0});
  while (!que.empty()) {
    int s = que.front(); que.pop();
    REP(b, B) {
      if (int nx = stone[s] ^ (1 << b); m.count(nx) == 1 && dist[m[nx]] == -1) {
        dist[m[nx]] = dist[s] + 1;
        que.emplace(m[nx]);
      }
    }
  }
  cout << (dist[n + 1] == -1 ? -1 : dist[n + 1] - 1) << '\n';
  return 0;
}