import itertools
import sys

input = sys.stdin.readline

N = int(input())
S = set(input() for _ in range(N))

anagrams = set()


def make_str(consonant, vowel, dup):
    s = ''
    dup_flag = True
    for i in range(11):
        if dup * 2 <= i:
            dup_flag = False
        if dup_flag ^ (i % 2):
            s += next(consonant)
        else:
            s += next(vowel)
    return s


for consonant in itertools.permutations(('n', 'b', 'm', 'g', 'r')):
    for vowel in itertools.permutations(('i', 'a', 'a', 'e', 'u', 'u')):
        for dup in range(6):
            anagrams.add(make_str(iter(consonant), iter(vowel), dup))

if N == len(anagrams):
    print('NO')
else:
    print((anagrams - S).pop())