#include <bits/stdc++.h>
#define MayaZayn ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
#define ll long long
#define endl '\n'
#define all(x) (x).begin(), (x).end()
#define all_r(x) (x).rbegin(), (x).rend()
#define mnEl(vec) *min_element(vec.begin(), vec.end())
#define mxEl(vec) *max_element(vec.begin(), vec.end())
#define yes cout << "YES"
#define no cout << "NO"
#define in(v) for (auto & x : v) cin >> x
#define out(v) for (auto & x : v) cout << x << ' '
#define inLL(v) for (ll & x : v) cin >> x
#define openIn(x) freopen(x, "r", stdin);
#define openOut(x) freopen(x, "w", stdout);
#define M 1000000007
#define N 100005

using namespace std;

void solve() {
    int n, a, b;
    cin >> n >> a >> b;
    bool mn = false, mx = false;
    for (int i = 0; i < n - 1; ++i) {
        int x;
        cin >> x;
        if (x == a)
            mn = true;
        if (x == b)
            mx = true;
    }

    if (!mn && !mx)
        cout << -1;
    else if (!mn)
        cout << a;
    else if (!mx)
        cout << b;
    else
        for (int i = a; i <= b; ++i)
            cout << i << endl;
}

int main() {
    MayaZayn

//    int t;
//    cin >> t;
//    while (t--)
        solve();

    return 0;
}