#include <iostream>
#include <algorithm>
#include <string>
#include <set>
using namespace std;
int main(){
   int N;
   cin >> N;
   set<string> S;
   for( int i = 0 ; i < N; i++ ){
      string s;
      cin >> s;
      S.insert(s);
   }
   string boin="aaeiuu";
   string siin="bgmnr";
   int p1[]={0,1,2,3,4};
   int p2[]={0,1,2,3,4};
   do{
      do{
         for( int pos=0 ; pos<6; pos++ ){
            string s="";
            for( int i=0; i<5; i++){
               if( i==pos ) s+= boin[5];
               s+=siin[p1[i]];
               s+=boin[p2[i]];
            }
            if( pos==5 ) s+= boin[5];
            if( S.find(s) == S.end() ){
               cout << s<< endl;
               return 0;
            }
         }

      }while( next_permutation(p2,p2+5) );
   }while( next_permutation(p1,p1+5) );
   cout << "NO"<<endl;
}