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):

            xs = []
            for i in range(5):
                xs.append(a[i])
                xs.append(b[i])

            last = b[-1]
            for i in range(5):
                ys = xs.copy()
                ys.insert(i * 2, last)

                t = ''.join(ys)
                if t not in used:
                    print(t)
                    return True

    return False


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