#!/usr/bin/env pypy3
# -*- coding: utf-8 -*-

import itertools


CONSONANTS = "nbmgr"
VOWELS = "iaaeuu"


def insert_char_after(base_string, char, index):
    if index == -1:
        return char + base_string
    else:
        return base_string[:index + 1] + char + base_string[index + 1:]


def solve(used_names):
    all_names = set()
    con_perms = itertools.permutations(CONSONANTS)
    vow_perms = itertools.permutations(VOWELS)
    for con_perm, vow_perm in itertools.product(con_perms, vow_perms):
        cons = "".join(con_perm)
        vows = "".join(vow_perm)
        vows_init = vows[0:5]
        vows_last = vows[-1]
        ten_str = "".join(a + b for a, b in zip(cons, vows))
        for i in range(-1, 10):
            all_names.add(insert_char_after(ten_str, vows_last, i))
    return all_names - used_names


def main():
    n = int(input())
    used_names = {input() for _ in range(n)}
    answers = solve(used_names)
    if not answers:
        print("NO")
    else:
        print(answers.pop())


if __name__ == '__main__':
    main()