#include <bits/stdc++.h>
using namespace std;
const long long INF = 1LL << 60;
const long long MOD = 1e9 + 7;
int cnt[13];
int ans;
void solve(int t, int bit) {
  if (t == 13) {
    int mi = 1 << 30;
    for (int i = 0; i < 24; i++) {
      if ((bit & (1 << i)) == 0) continue;
      for (int j = i + 1; j < 24; j++) {
        if ((bit & (1 << j)) == 0) continue;
        int d = abs(i - j);
        mi = min(mi, min(d, 24 - d));
      }
    }
    ans = max(ans, mi);
    return;
  }
  if (cnt[t] == 0) {
    solve(t + 1, bit);
    return;
  }
  if (cnt[t] == 1) {
    solve(t + 1, bit | (1 << t));
    solve(t + 1, bit | (1 << (24 - t)));
    return;
  }
  solve(t + 1, bit | (1 << t) | (1 << (24 - t)));
}
int main() {
  int N;
  cin >> N;
  cnt[0]++;
  for (int i = 0; i < (N); i++) {
    int D;
    cin >> D;
    cnt[D]++;
  }
  if (cnt[0] > 1 || cnt[12] > 1) {
    cout << 0 << endl;
    return 0;
  }
  for (int i = 1; i < 12; i++) {
    if (cnt[i] > 2) {
      cout << 0 << endl;
      return 0;
    }
  }
  solve(0, 0);
  cout << ans << endl;
}
