#include <iostream>
#include <vector>

using namespace std;

int solve(const vector<int>& times){
	if(times[0] >= 2 || times[12] >= 2) return 0;
	for(int i=1;i<12;i++) if(times[i] >= 3) return 0;
	int res = 0;
	for(int i=0;i<(1<<11);i++){
		vector<int> exist(25, 0);
		if(times[0] > 0) exist[0] = exist[24] = 1;
		if(times[12] > 0) exist[12] = 1;
		for(int j=1;j<12;j++){
			if(times[j] == 0) continue;
			if(times[j] == 1) exist[(i&(1<<(j-1))) ? j : 24-j] = 1;
			if(times[j] == 2) exist[j] = exist[24-j] = 1;
		}
		int pre = 0;
		int cur_res = 100;
		for(int j=1;j<=24;j++){
			if(exist[j]){
				cur_res = min(cur_res, j-pre);
				pre = j;
			}
		}
		res = max(res, cur_res);		
	}
	return res;
}

int main(){
	int N;
	while(cin >> N){
		vector<int> cnt(13, 0);
		cnt[0] = 1;
		for(int i=0;i<N;i++){
			int t; cin >> t;
			cnt[t]++;			
		}
		cout << solve(cnt) << endl;
	}
}
