#include <bits/stdc++.h>
using namespace std;
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++) {
        mi = min(mi, abs(time[j] - time[k]));
      }
    }
    ans = max(ans, mi);
  }
  cout << ans << endl;
  return 0;
}
