#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
#include <cstring>
#include <deque>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
#define CLR(mat) memset(mat, 0, sizeof(mat))
typedef long long ll;
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  int N; cin >> N;
  int cnt[13]; CLR(cnt);
  cnt[0] = 1;
  FOR(i,0,N) {
    int d; cin >> d;
    cnt[min(d, 24-d)]++;
  }
  if(cnt[0] >= 2 || cnt[12] >= 2) {
    cout << 0 << endl;
    return 0;
  }
  FOR(i,1,12) {
    if(cnt[i] >= 3) {
      cout << 0 << endl;
      return 0;
    }
  }
  int ans = 0;
  FOR(i,0,1<<11) {
    vector<int> v;
    v.push_back(0);
    if(cnt[12]) v.push_back(12);
    FOR(j,0,11) {
      // 1~11
      if(cnt[j+1] == 1) {
        if((i>>j)&1) v.push_back(j+1);
        else v.push_back(23-j);
      }
      else if(cnt[j+1] == 2) {
        v.push_back(j+1);
        v.push_back(23-j);
      }
    }
    sort(v.begin(), v.end());
    int mn = 1e9;
    FOR(i,0,v.size()) {
      //cout << v[i] << endl;
      int j = (i + 1) % v.size();
      mn = min(mn, min(abs(v[i]-v[j]), 24-abs(v[i]-v[j])));
    }
    ans = max(ans, mn);
  }
  cout << ans << endl;
  return 0;
}