#include <algorithm>
#include <cmath>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
#define U(v) cerr << #v << ": " << (v) << endl

int main() {
    int N;
    cin >> N;
    int D[13]{};
    for (int i = 0; i < N; ++i) {
        int d;
        cin >> d;
        ++D[d];
    }
    if (D[0] || D[12] >= 2) {
        cout << 0 << endl;
        return 0;
    }
    for (int d = 1; d < 12; ++d) {
        if (D[d] >= 3) {
            cout << 0 << endl;
            return 0;
        }
    }
    bool a[24]{};
    a[0] = true;
    vector<int> b;
    for (int d = 1; d < 12; ++d) {
        if (D[d] == 2)
            a[d] = a[24 - d] = true;
        else if (D[d] == 1)
            b.emplace_back(d);
    }
    if (D[12])
        a[12] = true;
    bool c[24];
    int mx = -1 << 30;
    for (int i = 0; i < (1 << b.size()); ++i) {
        copy_n(a, 24, c);
        for (int j = 0; j < (int)b.size(); ++j) {
            if ((i >> j) & 1) {
                c[24 - b[j]] = true;
            } else {
                c[b[j]] = true;
            }
        }
        int mn = 1 << 30;
        for (int j = 0; j < 24; ++j) {
            for (int k = j + 1; k < 24; ++k) {
                if (c[j] && c[k])
                    mn = min(mn, min(k - j, j - k + 24));
            }
        }
        mx = max(mx, mn);
    }
    cout << mx << endl;
    return 0;
}
