#include <bits/stdc++.h>

using namespace std;

char consonant[] = {'n', 'b', 'm', 'g', 'r'};
char vowel[] = {'i', 'a', 'a', 'e', 'u', 'u'};

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	sort(consonant, consonant + 5);
	sort(vowel, vowel + 6);
	set<string> candidate;
	do {
		do {
			string s[6] = {};
			for (int i = 0; i < 5; i++) {
				s[i] += vowel[5];
				for (int j = 0; j < 6; j++) {
					s[j] += consonant[i];
					s[j] += vowel[i];
				}
			}
			s[5] += vowel[5];
			for (int i = 0; i < 6; i++) {
				candidate.insert(s[i]);
			}
		} while (next_permutation(vowel, vowel + 6));
	} while (next_permutation(consonant, consonant + 5));

	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		string s;
		cin >> s;
		candidate.erase(s);
	}

	cout << (candidate.empty() ? "NO" : *candidate.begin()) << endl;
	return 0;
}