#include <bits/stdc++.h>
using namespace std;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))
#define EACH(it, c)         for(auto it=(c).begin();it!=(c).end();++it)

int main(){
    int N;
    cin >> N;
    set<string> S;
    REP(i,N){
        string s; cin >> s;
        S.insert(s);
    }

    string s0 = "nbmgr*";
    string s1 = "iaaeuu";
    sort(s0.begin(), s0.end());
    sort(s1.begin(), s1.end());

    do {
        do {
            string k;
            REP(i,6){
                if(s0[i] != '*') k += s0[i];
                k += s1[i];
            }
            if(S.count(k)) continue;
            cout << k << endl;
            return 0;
          
        } while(next_permutation(s1.begin(), s1.end()));
    } while(next_permutation(s0.begin(), s0.end()));

    cout << "NO" << endl;
    return 0;
}