#include "bits//stdc++.h"
using namespace std;
typedef long long ll;
const ll INF = 1LL << 60;
const ll MOD = 1e9 + 7;
#define rep(i,n) for (int i = 0; i < (n); i++)
#define ALL(v) v.begin(), v.end()
int cnt[13];
int ans;
void solve(int t, int bit) {
	if (t == 13) {
		int mi = 1 << 30;
		for (int i = 0; i < 24; i++) {
			if ((bit&(1 << i)) == 0) continue;
			for (int j = i + 1; j < 24; j++) {
				if ((bit&(1 << j)) == 0) continue;
				int d = abs(i - j);
				mi = min(mi, min(d, 24 - d));
			}
		}
		ans = max(ans, mi);
		return;
	}
	if (cnt[t] == 0) {
		solve(t + 1, bit);
		return;
	}
	if (cnt[t] == 1) {
		solve(t + 1, bit | (1 << t));
		if (t > 0) solve(t + 1, bit | (1 << (24 - t)));
		return;
	}
	solve(t + 1, bit | (1 << t) | (1 << (24 - t)));
}
int main() {
	int N;
	cin >> N;
	cnt[0]++;
	rep(i, N) {
		int D;
		cin >> D;
		cnt[D]++;
	}
	if (cnt[0] > 1 || cnt[12] > 1) {
		cout << 0 << endl;
		return 0;
	}
	for (int i = 1; i < 12; i++) {
		if (cnt[i] > 2) {
			cout << 0 << endl;
			return 0;
		}
	}
	solve(0, 0);
	cout << ans << endl;
}