#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cstdlib>

using namespace std;

int main(){
	ios_base::sync_with_stdio(false);
	int n;
	cin >> n;
	vector<int> h(13);
	++h[0];
	for(int i = 0; i < n; ++i){
		int di;
		cin >> di;
		++h[di];
	}
	if(h[0] >= 2 || h[12] >= 2){
		cout << 0 << endl;
		return 0;
	}
	for(int i = 1; i < 12; ++i){
		if(h[i] >= 3){
			cout << 0 << endl;
			return 0;
		}
	}
	int fixed = 0, variable = 0;
	if(h[0]  == 1){ fixed |= (1 << 12); }
	if(h[12] == 1){ fixed |= (1 <<  0); }
	for(int i = 1; i < 12; ++i){
		if(h[i] == 2){
			fixed |= (1 << (12 - i));
			fixed |= (1 << (12 + i));
		}else if(h[i] == 1){
			variable |= (1 << i);
		}
	}
	int answer = 0;
	for(int i = ((1 << 13) - 1) & variable; i >= 0; i = ((i - 1) & variable)){
		int set = fixed;
		for(int j = 0; j <= 12; ++j){
			if(variable & (1 << j)){
				if(i & (1 << j)){
					set |= (1 << (12 + j));
				}else{
					set |= (1 << (12 - j));
				}
			}
		}
		int s = 24;
		int last = __builtin_ctz(set);
		for(int j = last + 1; j < 24; ++j){
			if(set & (1 << j)){
				const int t = j - last;
				s = min(s, min(t, 24 - t));
				last = j;
			}
		}
		const int t = last - __builtin_ctz(set);
		if(t > 0){ s = min(s, min(t, 24 - t)); }
		answer = max(answer, s);
		if(i == 0){ break; }
	}
	cout << answer << endl;
	return 0;
}

