#include <bits/stdc++.h>
#define rep(i,n) for (int i=0; i<(n); ++i)
using namespace std;
using ll = long long;
using P = pair<int,int>;

int main(){
    int n;
    cin>>n;
    vector<bool>ok(12,true);
    vector<int>a[12];
    int d[7]={0,2,4,5,7,9,11};
    rep(i,12)rep(j,7){
        a[i].push_back((i+d[j])%12);
    }
    rep(i,n){
        int t;
        cin>>t;
        rep(j,12){
            bool exist=false;
            rep(k,7){
                if(a[j][k]==t)exist=true;
            }
            if(!exist)ok[j]=false;
        }
    }
    int cnt=0;
    rep(i,12)if(ok[i])cnt++;
    if(cnt==1){
        rep(i,12)if(ok[i])cout<<i<<endl;
    }
    else cout<<-1<<endl;
}