#include <iostream>
#include <vector>
#include <string>
#include <map>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

int N;
int s,t;
vector<int> st;
vector<vector<int>> E;
map<int,int> G;

int main(){
  cin >> N;
  st.resize(N+2);
  cin >> st[N] >> st[N+1];
  rep(i,N) cin >> st[i];
  E.resize(N+2);
  rep(i,N+2) G[st[i]] = i;
  rep(i,N+2) rep(d,30){
    int to = st[i] ^ (1<<d);
    if(G.find(to) == G.end()) continue;
    E[i].push_back(G[to]);
  }
  vector<int> I = {N};
  vector<int> D(N+2,-1);
  D[N] = 0;
  rep(i,I.size()){
    int p = I[i];
    for(int e : E[p]) if(D[e] == -1){
      D[e] = D[p] + 1;
      I.push_back(e);
    }
  }
  if(D[N+1] == -1) cout << "-1\n";
  else cout << (D[N+1]-1) << "\n";
  return 0;
}

struct ios_do_not_sync{
  ios_do_not_sync(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
  }
} ios_do_not_sync_inst;