N = int(input())
S = []
candi = set()
for _ in range(N):
    candi.add(input())
s = ["n","b","m","g","r",""]
b = ["i","a","a","e","u","u"]
#print(candi)

import itertools
ss = list(itertools.permutations(s))
bb = list(itertools.permutations(b))

for i in ss:
    for j in bb:
        ca = ""
        for k in range(6):
            ca+=i[k]+j[k]
        if ca not in candi:
            print(ca)
            exit()
print("NO")