#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> a(13, 0);
  a[0]++;
  for (int i = 0; i < n; i++) {
    int d;
    cin >> d;
    a[d]++;
    if ((n == 1 && d == 0) || a[d] > 2) {
      cout << 0 << endl;
      return 0;
    }
  }
  int ans = 0;
  for (int i = 0; i < 1 << 11; i++) {
    vector<int> tim;
    tim.push_back(0);
    if (a[12]) tim.push_back(12);
    for (int j = 0; j < 11; j++) {
      if (a[j + 1] == 0) continue;
      if (a[j + 1] == 2)
        tim.push_back(j + 1), tim.push_back(24 - j - 1);
      else if ((i >> j) & 1)
        tim.push_back(j + 1);
      else
        tim.push_back(24 - j - 1);
    }
    sort(tim.begin(), tim.end());
    int gap = 24 - tim[tim.size() - 1];
    for (int j = 1; j < tim.size(); j++) gap = min(gap, tim[j] - tim[j - 1]);
    ans = max(ans, gap);
  }
  cout << ans << endl;
  return 0;
}
