#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
#include <climits>
#include <vector>
#include <numeric>
#include <complex>
#include <map>
#include <bitset>
using namespace std;

//#define __int64 long long
#define long __int64
#define REP(i,a,b) for(int i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)
const int Vecy[4] = {0,-1,0,1};
const int Vecx[4] = {1,0,-1,0};


int main(){
	int n;
	vector<string> s;
	string in;
	string data1 = "aaeiuu";
	string data2 = "bgmnr";
	string check;
	char check1[6] = {'a','a','e','i','u','u'};
	char check2[5] = {'b','g','m','n','r'};
	bool flg = false;
	
	cin >> n;
	if(n == 0){
		cout << "inabameguru" << endl;
		return 0;
	}
	
	rep(i,n){
		cin >> in;
		s.push_back(in);
	}
	
	sort(s.begin(), s.end());
	
	do{
		rep(i,5){
			check2[i] = data2[i];
		}
		
		do{
			check = "";
			rep(i,5){
				check += check1[i];
				check += check2[i];
			}
			check += check1[5];
			
			if(!binary_search(s.begin(), s.end(), check)){
				cout << check << endl;
				flg = true;
			}
		
		}while( next_permutation(check2, check2 + 5) && !flg);
	}while( next_permutation(check1, check1 + 6) && !flg);
	
    if(!flg){
		cout << "NO" << endl;
    }
    return 0;
}