#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> d(n), cnt(13, 0);
  cnt[0] = 1;
  for (int i = 0; i < n; i++) {
    cin >> d[i];
    cnt[d[i]]++;
  }
  vector<int> t, t2;
  for (int i = 0; i <= 12; i++) {
    if (cnt[i] >= 3) {
      cout << 0 << endl;
      return 0;
    } else if (cnt[i] == 2) {
      t2.push_back(i);
      t2.push_back(24 - i);
    } else if (cnt[i] == 1) {
      t.push_back(i);
    }
  }
  int ans = 0;
  for (int i = 0; i < (1 << t.size()); i++) {
    vector<int> t3(t2);
    for (int j = 0; j < t.size(); j++) {
      if (i & (1 << j))
        t3.push_back(24 - t[j]);
      else
        t3.push_back(t[j]);
    }
    int hoge = 114514;
    for (int j = 0; j < t3.size(); j++) {
      for (int k = j + 1; k < t3.size(); k++) {
        int tmp = abs(t3[j] - t3[k]);
        hoge = min(hoge, tmp);
      }
    }
    ans = max(ans, hoge);
  }
  cout << ans << endl;
  return 0;
}
