#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<string>
#include<vector>
#include<list>
#include<queue>
#include<utility>
#include <fstream>
#include<set>
#include<map>
#include<cctype>
#include<cmath>
#include<algorithm>
using namespace std;


#define RALL(x) (x).rbegin(),(x).rend()
#define ALL(x) (x).begin(),(x).end()
#define repp(i,n) for(int (i)=1;(i)<=(n);(i)++)
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define clr(a) memset((a), 0 ,sizeof(a))

typedef pair<int,int> P;
typedef vector<pair<int,string> > pii;
typedef map<string,int> mdi;



int main(){
	int n;
	string s,s2;
	set<string> se;
	cin >> n;
	for(int i=0;i<n;i++){
		cin >> s;
		se.insert(s);
	}
	
	s="iaaeuu";
	s2="nbmgrz";
	sort(ALL(s));
	sort(ALL(s2));
	do{
		sort(ALL(s2));
		do{
			string ans="";
			for(int i=0;i<6;i++){
				ans+=s2.substr(i,1);
				ans+=s.substr(i,1);
			}
			for(int i=0;i<ans.size();i++){
				if(ans[i]=='z'){
					ans=ans.substr(0,i)+ans.substr(i+1);
					break;
				}
			}
			if(se.find(ans)==se.end()){
				cout << ans << endl;
				return 0;
			}
		}while(next_permutation(ALL(s2)));
	}while(next_permutation(ALL(s)));
	cout << "NO" << endl;
	return 0;
}