#include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(a); (i)<(b); ++(i))
#define rFor(i, a, b) for(int (i)=(a)-1; (i)>=(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
using namespace std;
typedef long long lint;

int main(){
    int n;
    scanf("%d", &n);
    int t[13];
    rep(i, 13) t[i] = 0;
    ++t[0];
    rep(i, n){
        int d = 0;
        scanf("%d", &d);
        ++t[d];
    }
    vector<int> a, b;
    rep(i, 13){
        if(t[i] > 2){
            printf("%d\n", 0);
            return 0;
        }
        if(t[i] == 2){
            a.push_back(i);
            a.push_back(-i);
        }
        if(t[i] == 1) b.push_back(i);
    }
    int ans = 0;
    int s = 30;
    rep(i, a.size())For(j, i+1, a.size()) s = min(s, min(abs(a[i]-a[j]), 24-abs(a[i]-a[j])));
    rep(i, 1<<b.size()){
        int tmp = min(30, s);
        rep(j, b.size())if((i>>j)&1) b[j] *= -1;
        rep(j, b.size()){
            For(k, j+1, b.size()) tmp = min(tmp, min(abs(b[k]-b[j]), 24-abs(b[k]-b[j])));
            rep(k, a.size()) tmp = min(tmp, min(abs(a[k]-b[j]), 24-abs(a[k]-b[j])));
        }
        ans = max(ans, tmp);
        rep(j, b.size()) b[j] = abs(b[j]);
    }
    printf("%d\n", ans);
}