#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> c(25);
  c[0] = 1;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    c[x]++;
  }
  c[24] = c[0];
  int p = 0;
  for (int i = 1; i <= 11; i++) {
    if (c[i] >= 1) {
      c[24 - i] = (c[i] + 1 - p) / 2;
      c[i] = (c[i] + p) / 2;
      p = 1 - p;
    }
  }
  int t = 1, ans = 24;
  for (int i = 1; i <= 24; i++) {
    if (c[i] >= 2) {
      ans = 0;
      break;
    } else if (c[i] == 1) {
      ans = min(ans, t);
      t = 1;
    } else {
      t++;
    }
  }
  cout << ans << endl;
  return 0;
}
