#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<set>
#include<string>
#include<algorithm>
#include<functional>
using namespace std;
#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 (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define INF 1<<30
#define MP make_pair
#define mp make_pair
#define pb push_back
#define PB push_back
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define ll long long
#define ull unsigned long long

int main(){
	int n;cin>>n;
	set<string> nos;
	REP(i,n){
		string no;cin>>no;
		nos.insert(no);
	}
	char c[]={'a','a','e','u','i','u'};
	char m[]={'n','b','m','g','r','~'};
	sort(c,c+6);
	sort(m,m+6);
	string s;
	do{
		do{
			s.clear();
			REP(i,6){
				if(m[i]!='~')s+=m[i];
				s+=c[i];
			}
			if(nos.count(s)==0){cout<<s<<endl;exit(0);}
		}while(next_permutation(m,m+6));
	}while(next_permutation(c,c+6));
	cout<<"NO"<<endl;
	return 0;
}