#include <iostream>
#include <vector>
#include <algorithm>
#include <unordered_set>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
using namespace std;
int main() {
    int n; cin >> n;
    unordered_set<string> s;
    repeat (i,n) {
        string t; cin >> t;
        s.insert(t);
    }
    string vowels = "aaeiuu";
    do {
        string consonants = "bgmnr";
        do {
            string t;
            repeat (i, vowels.length() + consonants.length()) {
                t += (i % 2 ? consonants : vowels)[i / 2];
            }
            if (not s.count(t)) {
                cout << t << endl;
                return 0;
            }
        } while (next_permutation(consonants.begin(), consonants.end()));
    } while (next_permutation(vowels.begin(), vowels.end()));
    cout << "NO" << endl;
    return 0;
}