#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> P;


int main()
{
    cin.tie(0);
    ios::sync_with_stdio(0);

    int N;
    cin >> N;
    int count[13];
    for (int i = 0; i <= 12; i++) {
        count[i] = 0;
    }
    count[0]++;
    int d;
    for (int i = 0; i < N; i++) {
        cin >> d;
        count[d]++;
    }

    if (count[0] > 1) {
        cout << 0 << endl;
        return 0;
    }
    for (int i = 1; i <= 12; i++) {
        if (count[i] > 2) {
            cout << 0 << endl;
            return 0;
        }
    }

    int ans = 0;
    for (int i = 0; i < (1<<12); i++) {
        vector<int> time;
        time.push_back(0);
        for (int j = 1; j <= 12; j++) {
            if (count[j] == 1) {
                if (i & (1 << j))
                    time.push_back(j);
                else
                    time.push_back(24 - j);
            } else if (count[j] == 2) {
                time.push_back(j);
                time.push_back(24 - j);
            }
        }

        int mi = INT_MAX;
        for (int j = 0; j < time.size(); j++) {
            for (int k = j + 1; k < time.size(); k++) {
                int d = abs(time[j] - time[k]);
                mi = min(mi, min(d, 24 - d));
            }
        }

        ans = max(ans, mi);
    }

    cout << ans << endl;

    return 0;
}
