#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>
#define llint long long

using namespace std;
typedef pair<llint, llint> P;
typedef pair<llint, P> E;

llint n;
llint cnt[13];
bool used[25];

int main(void)
{
	cin >> n;
	
	cnt[0] = 1;
	llint x;
	for(int i = 1; i <= n; i++){
		cin >> x;
		cnt[x]++;
	}
	for(int i = 0; i <= 12; i++){
		if(cnt[i] >= 3){
			cout << 0 << endl;
			return 0;
		}
	}
	if(cnt[0] >= 2 || cnt[12] >= 2){
		cout << 0 << endl;
		return 0;
	}
	
	int N = 1<<13, ans = 0;
	for(int i = 0; i < N; i++){
		for(int j = 0; j < 24; j++) used[j] = false;
		used[24] = true;
		for(int j = 1; j <= 12; j++){
			if(cnt[j] == 0) continue;
			if(cnt[j] == 2) used[j] = used[24-j] = true;
			if(cnt[j] == 1){
				if(i & (1<<j)) used[j] = true;
				else used[24-j] = true;
			}
		}
		//for(int j = 0; j <= 24; j++) cout << used[j] ; cout << endl;
		int cnt = 0, mn = 25;
		for(int j = 0; j <= 24; j++){
			if(used[j]) mn = min(mn, cnt), cnt = 0;
			cnt++;
		}
		ans = max(ans, mn);
	}
	cout << ans << endl;
	
	return 0;
}