from itertools import permutations
N = int(input())
a = [input() for i in range(N)]
vow = ["i","a","a","e","u","u"]
con = [" ","n","b","m","g","r"]
vow_all = set( permutations(vow))
con_all = set( permutations(con))

all_list = set()
for v in vow_all:
    for c in con_all:
        strings = ''
        for k in range(6):
            strings = strings + c[k] + v[k]
        all_list.add( strings.replace(' ','') )

a = set(a)
all_list -= a

if len(all_list) == 0:
    print('NO')
else:
    print('%s' % all_list.pop())