#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9 + 7;
int main() {
  int N;
  int D[50];
  int cnt[13];
  fill(cnt, cnt + 13, 0);
  cin >> N;
  for (int i = 0; i < N; i++) {
    cin >> D[i];
    cnt[D[i]]++;
  }
  if (cnt[0] == 1 || cnt[12] == 2) {
    cout << 0 << endl;
    return 0;
  } else {
    for (int i = 1; i < 12; i++) {
      if (cnt[i] >= 3) {
        cout << 0 << endl;
        return 0;
      }
    }
  }
  int ans = 0;
  for (int i = 0; i < (1 << 11); i++) {
    int diff = inf;
    vector<int> V;
    for (int j = 0; j < 11; j++) {
      if (cnt[j + 1] == 0) {
        continue;
      } else if (cnt[j + 1] == 1) {
        if ((i >> j) & 1) {
          V.push_back(j + 1);
        } else {
          V.push_back(24 - (j + 1));
        }
      } else {
        V.push_back(j + 1);
        V.push_back(24 - (j + 1));
      }
      diff = min(diff, min((j + 1), 24 - (j + 1)));
    }
    if (cnt[12] == 1) {
      V.push_back(12);
      diff = min(diff, 12);
    }
    sort(V.begin(), V.end());
    for (int j = 0; j < N - 1; j++) {
      diff = min(diff, abs(V[j] - V[j + 1]));
    }
    diff = min(diff, abs(V[0] - V[N - 1]));
    ans = max(ans, diff);
  }
  cout << ans << endl;
  return 0;
}
