#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#include <list>
#include <atcoder/all>
#define popcount __builtin_popcount
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<int, int> P;

int main()
{
    int n;
    cin>>n;
    map<int, int> mp;
    int a[50050];
    cin>>a[0]>>a[n+1];
    mp[a[0]]=0, mp[a[n+1]]=n+1;
    for(int i=1; i<n+1; i++){
        cin>>a[i];
        mp[a[i]]=i;
    }
    const int INF=1e9;
    int d[50050];
    fill(d, d+n+2, INF);
    d[0]=0;
    queue<int> que;
    que.push(0);
    while(!que.empty()){
        int x=que.front(); que.pop();
        for(int i=0; i<30; i++){
            int b=(a[x]^(1<<i));
            if(mp.find(b)!=mp.end()){
                int y=mp[b];
                if(d[y]>d[x]+1){
                    d[y]=d[x]+1;
                    que.push(y);
                }
            }
        }
    }
    if(d[n+1]==INF) cout<<-1<<endl;
    else cout<<d[n+1]-1<<endl;
    return 0;
}