from itertools import permutations
name = set()
add, diff = name.add, name.difference_update
consonant = ["", "n", "b", "m", "g", "r"]
vowel = ["i", "a", "a", "e", "u", "u"]
for a, c, e, g, i, k in permutations(consonant):
    for b, d, f, h, j, l in permutations(vowel):
        add(a+b+c+d+e+f+g+h+i+j+k+l)

n = int(input())
name2 = []
append = name2.append
for _ in [0]*n:
    append(input())

name.difference_update(name2)
print(name.pop() if name else "NO")