#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
using namespace std;

#define REP(i,s,e) for (i = s; i <= e; i++)
#define rep(i,n) REP (i,0,(int)(n)-1)
#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP (i,(int)(n)-1,0)
#define INF (int)1e8
#define MOD (int)(1e9+7)

typedef long long ll;

int cnt[11][256];

int main(void) {
    int i, j, n;
    int order[6];
    set<string> st;
    string s;
    cin >> n;
    while (n--) {
        cin >> s;
        st.insert(s);
    }
    rep (i,6) order[i] = i;
    s = "aabegimnruu";
    rep (j,6) {
        string vowel = "aaeiuu";
        do {
            string consonant = "bgmnr";
            do {
                string s;
                int pos = 0;
                rep (i,6) {
                    if (j != i)
                        s.push_back(consonant[pos++]);
                    s.push_back(vowel[i]);
                }
                if (!st.count(s)) {
                    cout << s << endl;
                    return 0;
                }
            } while (next_permutation(consonant.begin(),consonant.end()));
        } while (next_permutation(vowel.begin(),vowel.end()));
    }
    cout << "NO" << endl;
    return 0;
}