import itertools as itr

N = int(input())
S = [input() for i in range(N)]

for a in itr.permutations(['i', 'a', 'a', 'e', 'u', 'u'], 6):
    for b in itr.permutations(['n', 'b', 'm', 'g', 'r'], 5):
        s = ""
        for i in range(5):
            s += a[i] + b[i]
        s += a[5]
        if not s in S:
            print(s)
            exit()

print('NO')