#include <iostream>
using namespace std;
int n, cnt[13];
bool H[25];

int count() {
    int i = 0, j = -1, ans = 24;
    while (i < 25) {
        if (H[i]) {
            if (j >= 0) ans = min(ans, i-j);
            j = i;
        }
        i++;
    }
    return ans;
}

int solve(int h) {
    if (h == 12) {
        if (cnt[h] > 0) H[h] = true;
        int a = count();
        H[h] = false;
        return a;
    } else {
        if (cnt[h] == 0) return solve(h+1);
        else if (cnt[h] == 1) {
            H[h] = true;
            int a1 = solve(h+1);
            H[h] = false;
            H[24-h] = true;
            int a2 = solve(h+1);
            H[24-h]= false;
            return max(a1, a2);
        } else if (cnt[h] == 2) {
            H[h] = H[24-h] = true;
            int a = solve(h+1);
            H[h] = H[24-h] = false;
            return a;
        } else return 0;
    }
}

int main() {
    cin >> n;
    for (int i = 0; i < n; i++) {
        int h; cin >> h;
        cnt[h]++;
    }
    H[0] = H[24] = true;
    if (cnt[0] > 0 || cnt[12] > 1) { cout << "0\n"; }
    else cout << solve(1) << endl;
}
