#include <bits/stdc++.h>
using namespace std;
int ss[13], n, bb[13], tt[5];
inline int cc(int xx) {
  for (int i = 0; i < 13; i++)
    if (ss[i] >= 3) return 0;
  int bb = 30;
  for (int i = 0; i < 13; i++)
    if (ss[i] == 2) bb = min(bb, min(2 * i % 24, 24 - 2 * i % 24));
  for (int i = 0; i < 13; i++)
    if (ss[i]) {
      for (int j = i + 1; j < 13; j++)
        if (ss[j]) {
          tt[0] = 0;
          if (ss[i] == 2)
            tt[++tt[0]] = i, tt[++tt[0]] = -i;
          else
            tt[++tt[0]] = i * (xx & (1 << i) ? -1 : 1);
          if (ss[j] == 2)
            tt[++tt[0]] = j, tt[++tt[0]] = -j;
          else
            tt[++tt[0]] = j * (xx & (1 << j) ? -1 : 1);
          for (int t = 1; t <= tt[0]; t++)
            for (int s = t + 1; s <= tt[0]; s++)
              bb = min(bb, min(abs(tt[t] - tt[s]) % 24,
                               24 - abs(tt[t] - tt[s]) % 24));
        }
    }
  return bb;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    int k;
    scanf("%d", &k);
    ss[k]++;
  }
  if (n == 1) {
    puts("0");
    return 0;
  }
  int ans = 0;
  for (int i = 0; i < (1 << 14); i++) ans = max(ans, cc(i));
  cout << ans << endl;
  return 0;
}
