#include<bits/stdc++.h>
using namespace std;

int main(int argc, char *argv[]){
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  set<string> used;
  for (int i = 0; i < n; i++) {
    string tmp;
    cin >> tmp;
    used.insert(tmp);
  }
  string vowel = "aaeiuu";
  string consonant = "bgmnr";
  sort(consonant.begin(), consonant.end());
  sort(vowel.begin(), vowel.end());
  do{
    do{
      for (int i = 0; i < 6; i++) {
        string ans;
        int seq = 0;
        for (int j = 0; j < 5; j++) {
          if(i == j){
            ans += vowel[j];
            seq++;
          }
          ans += consonant[j];
          ans += vowel[j + seq];
        }
        if(seq == 0)ans += vowel.back();
        if(used.count(ans) == 0){
          std::cout << ans << std::endl;
          return 0;
        }
      }
    }while(next_permutation(consonant.begin(), consonant.end()));
  }while(next_permutation(vowel.begin(), vowel.end()));
  std::cout << "NO" << std::endl;
  return 0;
}