#define _USE_MATH_DEFINES

#include <iostream>
#include <iomanip>

#include <algorithm>
#include <cmath>

#include <string>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>

/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////
const int inmax = (518400/4);
string name[inmax];
set<string> nameSet;
int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(6);//
	//１母音どこでもいいああ
	LL N;
	cin>>N;
	if(N>=inmax){
		P("NO");
		return 0;
	}
	else if(N==0){
		P("inabameguru");
		return 0;
	}
	rep(i,N){
		cin>>name[i];
		nameSet.insert(name[i]);
	}
	///////////////
	
	vector<char> si;
	si.push_back('n');
	si.push_back('b');
	si.push_back('m');
	si.push_back('g');
	si.push_back('r');

	vector<char> bo;
	bo.push_back('a');
	bo.push_back('a');
	bo.push_back('i');
	bo.push_back('u');
	bo.push_back('u');
	bo.push_back('e');

	string temp;
	int count;
	pair<set<string>::iterator,bool> kekka;
	do{
		do{
			for(int k=0;k<6;++k){
				for(int i=0;i<5;++i){
					if(i==k){
						temp += (bo[5]);
					}
					temp += (si[i]);
					temp += (bo[i]);
				}
				if(k==5){
					temp += (bo[5]);
				}
				kekka = nameSet.insert(temp);
				if(kekka.second == true){
					P( *(kekka.first) );
					return 0;
				}
				/*
				count = 0;
				for(int i=0;i<N;++i){//129600
					if(temp != name[i] ){
						++count;
					}else{
						break;
					}
				}
				if(count == N){
					//P(temp);
//					return 0;
				}
				*/
				temp = "";
			}
		}while( next_permutation(bo.begin(), bo.end()) );
	}while( next_permutation(si.begin(), si.end()) );
	P("NO");
	return 0;
}