#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
using namespace std;
using pii = pair<int, int>;

bool cmp(const pii& p, int key){
    return p.first<key;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N; cin>>N;
    int st, en; cin>>st>>en;
    vector<pii> vertex = {{st, 0}, {en, 1}};
    vector<int> stones(N+2);
    stones[0]=st, stones[1]=en;
    for (int i=2;i<N+2;i++){
        int stone; cin>>stone;
        stones[i]=stone;
        vertex.push_back({stone, i});
    }

    sort(vertex.begin(), vertex.end());

    vector<int> D(N+2, -1);
    D[0]=0;
    queue<int> Q;
    Q.push(0);
    while(! Q.empty()){
        int cur = Q.front();
        Q.pop();
        for (int i=0;i<30;i++){
            int next = stones[cur] ^ (1<<i);
            auto it = lower_bound(vertex.begin(), vertex.end(), next, cmp);
            if (it != vertex.end() && it->first==next){
                if (D[it->second]!=-1) continue;
                D[it->second] = D[cur]+1;
                Q.push(it->second);
            }
        }
    }
    cout << (D[1]!=-1 ? D[1]-1 : -1) << "\n";
    return 0;
}