#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

using ll = long long;

ll gcd(ll x, ll y) {
    if (y == 0) return x;
    return gcd(y, x % y);
}

int main() {
    int N;
    cin >> N;
    vector<int> A(N);
    ll g = 0;
    for (int i = 0; i < N; i++) {
        cin >> A[i];
        if (A[i] != -1) {
            g = gcd(g, A[i]);
        }
    }
    if (g == 0) {
        cout << -1 << endl;
    } else {
        cout << g * g << endl;
    }
}