#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  int all[N];
  int x[13] = {0};
  for (int i = 0; i < N; i++) cin >> all[i];
  for (int i = 0; i < N; i++) {
    x[all[i]] += 1;
  }
  bool check;
  for (int i = 0; i < 13; i++) {
    if (x[i] > 2) check = false;
  }
  int ans = 0;
  if (check) {
    vector<int> test;
    for (int i = 0; i < 1 << 13; i++) {
      test.clear();
      for (int j = 0; j < 13; j++) {
        if ((i >> j & 1) == 1 && x[j] == 1)
          test.push_back(j);
        else if ((i >> j & 1) == 0 && x[j] == 1)
          test.push_back((24 - j));
        else if (x[j] == 2) {
          test.push_back(j);
          test.push_back((24 - j));
        }
      }
      test.push_back(0);
      test.push_back(24);
      sort(test.begin(), test.end());
      int temp = 24;
      for (int j = 0; j < test.size() - 1; j++)
        temp = min(temp, test[j + 1] - test[j]);
      ans = max(ans, temp);
    }
    cout << ans << endl;
  } else
    cout << 0 << endl;
  return 0;
}
