from itertools import permutations

consonants = 'nbmgr'
vowels = 'iaaeuu'

N = int(input())
SS = [input() for _ in range(N)]


def solve():
    used = set(SS)
    for a in permutations(consonants):
        for b in permutations(vowels):
            for i in range(5):
                c = b[0]
                cs = []
                for j, ab in enumerate(zip(a, b[1:])):
                    if i == j:
                        cs.append(c)
                    cs.append(ab[0])
                    cs.append(ab[1])

                s = ''.join(cs)
                if s not in used:
                    print(s)
                    return True

    return False


found = solve()
if not found:
    print('NO')