#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>
#include <set>

using namespace std;

int main() {
	int n;
	string name;

	cin >> n;

	set<string> names;
	for (int i = 0; i < n; i++) {
		cin >> name;
		names.insert(name);
	}

	string boin  =  "nbmgr";
	string shiin = "iaaeuu";
	int n_boin = boin.size();
	int n_shiin = shiin.size();

	sort(boin.begin(), boin.end());
	sort(shiin.begin(), shiin.end());

	do {
		do {
			for (int i = 0; i < n_shiin; i++) {
				name.clear();
				int idx_b = 0;

				for (int j = 0; j < n_shiin; j++) {
					if (j != i) {
						name += boin[idx_b];
						idx_b++;
					}
					name += shiin[j];
				}

				if (names.count(name) == 0) {
					cout << name << endl;
					return 0;
				}
			}

		} while (next_permutation(boin.begin(), boin.end()));
	} while (next_permutation(shiin.begin(), shiin.end()));

	cout << "NO" << endl;
	return 0;
}