#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
    int n;
    cin >> n;
    vector<int> a(13, 0);   a[0]++;
    for(int i = 0; i < n; i++){
        int d;  cin >> d;
        a[d]++;
        if((n == 1 && d == 0) || a[d] > 2){
            cout << 0 << endl;
            return 0;
        }
    }
    if(a[0] == 2){
        cout << 0 << endl;
        return 0;
    }
    int ans = 0;
    for(int i = 0; i < 1<<11; i++){
        vector<int> tim;
        tim.push_back(0);
        if(a[12])   tim.push_back(12);
        for(int j = 0; j < 11; j++){
            if(a[j+1] == 0)   continue;
            if(a[j+1] == 2)   tim.push_back(j+1), tim.push_back(24-j-1);
            else if((i>>j)&1) tim.push_back(j+1);
            else              tim.push_back(24-j-1);
        }
        sort(tim.begin(), tim.end());
        int gap = 24-tim[tim.size()-1];
        for(int j = 1; j < tim.size(); j++) gap = min(gap, tim[j]-tim[j-1]);
        ans = max(ans, gap);
    }
    cout << ans << endl;
    return 0;
}