#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    int n;
    cin >> n;
    set<string> s;
    for(int i=0; i<n; ++i){
        string t;
        cin >> t;
        s.insert(t);
    }

    string consonant = "bgmnr";
    string vowel     = "aaeiuu";
    do{
        do{
            for(int k=0; k<6; ++k){
                string t(10, ' ');
                for(int i=0; i<5; ++i){
                    t[2*i] = consonant[i];
                    t[2*i+1] = vowel[i];
                }
                t.insert(t.begin() + 2 * k, vowel[5]);

                if(s.find(t) == s.end()){
                    cout << t << endl;
                    return 0;
                }
            }
        }while(next_permutation(vowel.begin(), vowel.end()));
    }while(next_permutation(consonant.begin(), consonant.end()));

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