from itertools import permutations as perm
N = int(raw_input())
used = set([raw_input() for i in range(N)])
con = ["n","b","m","g","r"]
vow = set(perm(["i","a","a","e","u","u"]))
for v in vow:
	cv = [p[0]+p[1] for p in zip(con,v)] + [v[5]]
	for nl in perm(cv):
		n = "".join(nl)
		if n not in used:
			print n
			quit()
print "NO"