#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);
  }
  char vowel[] = {'i', 'a', 'a', 'e', 'u', 'u'};
  char consonant[] = {'n', 'b', 'm', 'g', 'r'};
  sort(consonant, consonant + 5);
  sort(vowel, vowel + 6);
  bool ok;
  string ans;
  char tmp;
  do{
    do{
      ok = true;
      for (int i = 0; i < 6; i++) {
        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[5];
        if(used.find(ans) != used.end())
          ok = false;
        if(ok){
          std::cout << ans << std::endl;
          return 0;
        }
      }
    }while(next_permutation(consonant, consonant + 5));
  }while(next_permutation(vowel, vowel + 6));
  std::cout << "NO" << std::endl;
  return 0;
}