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

int main(){
   set<string> s;
   int n;
   cin >> n;
   for(int i = 0;i < n;i++){
      string str;
      cin >> str;
      s.insert(str);
   }
   string a = "iaaeuu",b = "nbmgr";
   stable_sort(a.begin(),a.end());
   stable_sort(b.begin(),b.end());
   do{
      do{
         string tmp = "          ";
         for(int i = 0;i < 5;i++){
            tmp[i * 2] = b[i];
            tmp[i * 2 + 1] = a[i];
         }
         for(int i = 0;i < 11;i++){
            string str = tmp.substr(0,i) + a[5] + tmp.substr(i);
            if(!s.count(str)){
               cout << str << endl;
               return 0;
            }
         }
      }while(next_permutation(b.begin(),b.end()));
   }while(next_permutation(a.begin(),a.end()));
   cout << "NO" << endl;
}