#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;
int main(){
  vector<char> v1={'a','a','e','i','u','u'};
  vector<char> v2={'b','g','m','n','r'};
  vector<string> v3;
  for(int i=0;i<v1.size();++i){
    if(i!=1 && i!=5){
    vector<char> v4=v1;
    char a=v4[i];
    v4.erase(v4.begin()+i);
    do{
      vector<char> v5=v2;
      do{
         string s1;
         for(int j=0;j<v5.size();++j){
           s1+=v5[j];
           s1+=v4[j];
         }
         for(int j=0;j<=s1.size();j+=2){
           string s2=s1;
           s2.insert(s2.begin()+j,a);
           v3.push_back(s2);
         }
      } while(next_permutation(v5.begin(),v5.end()));
    } while(next_permutation(v4.begin(),v4.end()));
    }
  }
  int N;cin>>N;
  set<string> s;
  string S;
  for(int i=0;i<N;++i){
    cin>>S;
    s.insert(S);
  }
  int ss1=s.size();
  int f=0;
  for(int i=0;i<v3.size();++i){
    s.insert(v3[i]);
    int ss2=s.size();
    if(ss2>ss1){
      cout<<v3[i];
      f=1;
      break;
    }
  }
  if(f==0){
    cout<<"NO";
  }
}