#include "bits/stdc++.h"
using namespace std;

#define nl "\n"
#define ll long long
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define sz(v) (int) v.size()

template<typename T = int>
istream &operator>>(istream &in, vector<T> &v) {
    for (auto &x: v) in >> x;
    return in;
}

template<typename T = int>
ostream &operator<<(ostream &out, const vector<T> &v) {
    for (const T &x: v) out << x << " ";
    return out;
}

void Sira() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}

void solve(){
    int n , a , b;
    cin >> n >> a >> b;

    bool ok_a = false , ok_b = false;

    for(int i = 0 ; i < n - 1 ; i++){
        int x;
        cin >> x;
        if(x == a) ok_a = true;
        if(x == b) ok_b = true;
    }

    if(ok_a and ok_b){
        for(int i = a ; i <= b ; i++){
            cout << i << nl;
        }
    }else if(!ok_a and !ok_b){
        cout << -1 << nl;
    }else{
        if(!ok_a){
            cout << a << nl;
        }else{
            cout << b << nl;
        }
    }
}

int main() {
    Sira();
    int t = 1;
//    cin >> t;
    while(t--){
        solve();
    }
    return 0;
}