#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
#include <cmath>

#define FORR(i,b,e) for(int i=(b);i<(int)(e);++i)
#define FOR(i,e) FORR(i,0,e)
#define sortuniq(v) sort(v.begin(), v.end()), v.erase(unique(v.begin(),v.end()),v.end())
#define dump(var) cerr << #var ": " << var << "\n"
#define dumpc(con) for(auto& e: con) cerr << e << " "; cerr<<"\n"

typedef long long ll;
typedef unsigned long long ull;

const double EPS = 1e-6;
const int d4[] = {0, -1, 0, 1, 0};

using namespace std;


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int N;
    cin >> N;
    if (N >= 129600) {
        cout << "NO" << endl;
        return 0;
    }
    set<string> used;
    FOR(i, N) {
        string S;
        cin >> S;
        used.insert(S);
    }
    
    string vowel = "iaaeuu";
    string consonant = "nbmgr";
    string new_name;
    sort(vowel.begin(), vowel.end());
    sort(consonant.begin(), consonant.end());
    do {
        do {
            FOR(p, 6) {
                new_name.clear();
                FOR(i, 6) {
                    if (i < p) new_name.push_back(consonant[i]);
                    else if (p < i) new_name.push_back(consonant[i-1]);
                    new_name.push_back(vowel[i]);
                }
                if (used.find(new_name) == used.end()) {
                    goto finish;
                }
                else {
                    continue;
                }
            }
        } while (next_permutation(consonant.begin(), consonant.end()));
    } while(next_permutation(vowel.begin(), vowel.end()));

    finish:
    cout << new_name << endl;

    return 0;
}