import itertools

voewl=['i','a','a','e','u','u']
consonant=['','n','b','m','g','r']
vs = set(itertools.permutations(voewl))
cs = set(itertools.permutations(consonant))
sn=set()
all=set()

n=int(input())
for i in range(n):
  sn.add(input())

for i in vs:
  for j in cs:
    str=''
    for k in range(6):
      str = str+j[k]+i[k]
    all.add(str)

if len(all)==n:
  print('NO')
else:
  all-=sn
  print(all.pop())