#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<int(n);++i)
#define debug(x) cout<<#x<<": "<<x<<endl

int n;
map<int, int> mp;
int res = 1;
bool det[24]={};

void rec(int k){
    if(k==12){
        int ans = 12;
        rep(i,24)rep(j,i){
            if(det[i] && det[j]){
                ans = min(ans,min(24-i+j,i-j));
            }
        }
        res = max(res,ans);
        return;
    }
    if(mp[k]==1){
        det[k] = true;
        rec(k+1);
        det[k] = false;
        det[24-k] = true;
        rec(k+1);
        det[24-k] = false;
    }else{
        rec(k+1);
    }
}

int solve(){
    cin>>n;
    mp[0]++;
    rep(i,n){
        int d;
        cin>>d;
        mp[d]++;
        if(mp[d] >= 3) return 0;
    }
    if(mp[0] >= 2 || mp[12] >= 2) return 0;
    
    det[0] = true;
    if(mp[12]==1) det[12] = true;
    rep(i,12) if(mp[i]==2) det[i] = det[24-i] = true;
    rec(1);
    return res;
}

int main(void){
    cout<<solve()<<endl;
    return 0;
}
