#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    int n;
    cin >> n;

    int p[7] = { 0,2,4,5,7,9,11 };
    int s[12] = {};
    for (int i = 0; i < 7; i++) {
        s[p[i]]++;
    }

    int q[12] = {};
    for (int i = 0; i < n; i++) {
        int t;
        cin >> t;

        q[t] = 1;
    }

    int r = -1;
    for (int j = 0; j < 12; j++) {
        int b = 1;
        for (int i = 0; i < 12; i++) {
            if (q[(i + j) % 12] && !s[i]) b = 0;
        }
        if (b) {
            if (r >= 0) {
                cout << -1 << endl;
                exit(0);
            }
            r = j;
        }
    }

    cout << r << endl;

    return 0;
}