#include <bits/stdc++.h>
#define FOR(i, a, b) for(int i=(int)(a); i!=(int)(b); i++)
#define RFOR(i, a, b) for(int i=(int)(a); i!=(int)(b); i--)
#define REP(i, n) FOR(i, 0, n)
using namespace std;
using ll = long long;

int dis(int a, int b){
  return min(abs(a-b), 24-abs(a-b));
}

int main(){
  int n; cin >> n;
  int d[n], ci[13]{}, cl[24]{};
  ci[0] = 1;
  REP(i, n){
    cin >> d[i];
    ci[d[i]]++;
  }

  int ans = 0;
  REP(i, 1<<13){
    bitset<13> b(i);

    //2^11のパターンを構築
    memset(cl, 0, sizeof(cl));
    REP(j, 13){
      if(ci[j] == 1){
        if(b[j]) cl[j] = 1;
        else cl[(24-j)%24] = 1;
      }
      else if(ci[j] == 2){
        if(j == 0 || j == 12){
          cout << 0 << endl;
          return 0;
        }
        cl[j] = cl[(24-j)%24] = 1;
      }
      else if(ci[j] > 2){
        cout << 0 << endl;
        return 0;
      }
    }

    //実際に最小値を計算
    int t = 24;
    REP(j, 24)REP(k, 24){
      if(j != k && cl[j] && cl[k]){
        t = min(t, dis(j, k));
      }
    }

    ans = max(t, ans);
  }

  cout << ans << endl;

  return 0;
}
