#include <iostream>
#include <cmath>
#include <climits>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <functional>
#include <algorithm>
#include <sstream>
#include <map>
#include <set>
#include <utility>

#define endl '\n'
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define DEBUG(x) cout<<#x<<": "<<x<<endl

using namespace std;

typedef pair<int,int> P;
typedef long long int LL;

const int isz=11;
string bo="iaaeuu";
string si="nbmgr";

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n;
	sort(ALL(si));
	sort(ALL(bo));
	cin>>n;
	set<string> s;
	REP(i,n){
		string in;
		cin>>in;
		s.insert(in);
	}
	do{
		do{
			string str;
			int ps=0;
			int pb=0;
			REP(i,isz-1){
				if(i%2==1){
					str+=bo[pb++];
				}else{
					str+=si[ps++];
				}
			}
			str+=bo[pb++];
			if(s.find(str)==s.end()){
				cout<<str<<endl;
				return 0;
			}
			pb=0;
			ps=0;
			str="";
			REP(i,isz){
				if(i%2==0){
					str+=bo[pb++];
				}else{
					str+=si[ps++];
				}
			}
			if(s.find(str)==s.end()){
				cout<<str<<endl;
				return 0;
			}
		}while(next_permutation(ALL(si)));
	}while(next_permutation(ALL(bo)));
	cout<<"NO"<<endl;
	return 0;
}