#include<bits/stdc++.h>
#define int long long
using namespace std;
#define rep(i,n) for(int i=0;i<(n);++i)
#define INF (1ll<<60)
typedef pair<int, int> pii;
#define FI first
#define SE second
#define all(s) s.begin(),s.end()
#define RREP(i,n) for(int i=(n)-1;i>=0;--i)

int N;
set<string> S;

void rekkyo() {
	string bo = "aaeiuu";
	string si = "bgmnr";
	do {
		do {
			rep(i,5)
			{
				string t;
				rep(j,5)
				{
					if (i == j)
						t += bo[5];
					t += si[j];
					t += bo[j];
				}
				if (!S.count(t)) {
					cout << t << endl;
					return;
				}
			}
		} while (next_permutation(all(si)));
	} while (next_permutation(all(bo)));
	cout << "NO" << endl;
}

signed main() {
	cin >> N;
	rep(i,N)
	{
		string s;
		cin >> s;
		S.insert(s);
	}
	rekkyo();
}