#include <bits/stdc++.h>
using namespace std;
int a[55];
int b[15];
int q[100], r[100];
int ans, cnt;
void dfs(int k) {
  if (k == 13) {
    for (int i = 1; i <= cnt; i++) r[i] = q[i];
    sort(r + 1, r + 1 + cnt);
    int minx = 10086;
    for (int i = 1; i <= cnt - 1; i++) minx = min(minx, r[i + 1] - r[i]);
    ans = max(ans, minx);
    return;
  }
  if (b[k] == 0) dfs(k + 1);
  if (b[k] == 1) {
    cnt++;
    q[cnt] = k;
    dfs(k + 1);
    cnt--;
    cnt++;
    q[cnt] = 24 - k;
    dfs(k + 1);
    cnt--;
  }
  if (b[k] == 2) {
    cnt++;
    q[cnt] = k;
    cnt++;
    q[cnt] = k;
    dfs(k + 1);
    cnt -= 2;
    cnt++;
    q[cnt] = 24 - k;
    cnt++;
    q[cnt] = k;
    dfs(k + 1);
    cnt -= 2;
    cnt++;
    q[cnt] = 24 - k;
    cnt++;
    q[cnt] = 24 - k;
    dfs(k + 1);
    cnt -= 2;
  }
}
int main() {
  int N;
  cin >> N;
  for (int i = 1; i <= N; i++) {
    cin >> a[i];
    b[a[i]]++;
  }
  for (int i = 0; i <= 12; i++) {
    if (b[i] > 2) {
      cout << 0 << endl;
      return 0;
    }
  }
  cnt = 1;
  q[1] = 0;
  if (b[0]) {
    cout << 0 << endl;
    return 0;
  }
  dfs(1);
  cout << ans << endl;
  return 0;
}
