#include <bits/stdc++.h>
using namespace std;
int N, d, c[15], bit;
bool f[29], ff[29];
int main() {
  cin >> N;
  for (int i = 0; i < N; i++) cin >> d, c[d]++;
  f[0] = true;
  bool flag = false;
  for (int i = 0; i <= 12; i++) {
    if (i == 0 && c[i] >= 1)
      flag = true;
    else if (i == 12 && c[i] >= 2)
      flag = true;
    else if (c[i] >= 3)
      flag = true;
    if (i == 12 && c[i] == 1) f[12] = true;
    if (1 <= i && i <= 11 && c[i] == 2) f[c[i]] = c[24 - c[i]] = true;
  }
  for (int i = 1; i < 12; i++) {
    if (c[i] == 1) bit |= 1 << i;
  }
  if (flag)
    cout << 0 << endl;
  else {
    int ret = 0;
    for (int i = 0; i < 1 << 12; i++) {
      if ((i | bit) != bit) continue;
      for (int j = 0; j < 24; j++) ff[j] = f[j];
      for (int j = 1; j < 12; j++) {
        if (c[j] != 1) continue;
        if (i & (1 << j))
          ff[j] = true;
        else
          ff[24 - j] = true;
      }
      int res = 1 << 30;
      for (int j = 0; j < 24; j++) {
        for (int k = j + 1; k < 24; k++) {
          if (ff[j] && ff[k]) res = min(res, min(k - j, 24 - k + j));
        }
      }
      ret = max(ret, res);
    }
    cout << ret << endl;
  }
  return 0;
}
