#include <bits/stdc++.h>
using namespace std;
int n, d[13], mem, mx, mem2;
bool p[24], memp[24];
int main() {
  cin >> n;
  for (int i = 0; i < 12; i++) d[i] = 0;
  for (int i = 0; i < n; i++) {
    cin >> mem;
    if (mem == 0) {
      cout << 0 << endl;
      return 0;
    }
    d[mem]++;
  }
  if (d[0] >= 1 || d[12] >= 2) {
    cout << 0 << endl;
    return 0;
  }
  for (int i = 0; i < 24; i++) p[i] = false;
  p[0] = true;
  if (d[12] == 1) p[12] = true;
  for (int i = 0; i < 12; i++) {
    if (d[i] >= 3) {
      cout << 0 << endl;
      return 0;
    }
    if (d[i] == 2) {
      p[i] = p[24 - i] = true;
    }
  }
  mx = 0;
  for (int i = 0; i < (1 << 12) - 1; i++) {
    for (int j = 0; j < 24; j++) memp[j] = p[j];
    mem = i;
    for (int j = 0; j < 12; j++) {
      if (d[j] == 1) {
        if (mem % 2 == 1)
          memp[j] = true;
        else
          memp[(24 - j) % 24] = true;
      }
      mem /= 2;
    }
    mem = -10000;
    mem2 = 100;
    for (int j = 0; j < 24; j++) {
      if (memp[j]) {
        mem2 = min(mem2, j - mem);
        mem = j;
      }
      min(mem2, 24 - mem);
    }
    mx = max(mx, mem2);
  }
  cout << mx << endl;
  return 0;
}
