from math import factorial as fact
from itertools import permutations as perm
N = int(raw_input())
used = set([raw_input() for i in range(N)])
if N >= fact(6)**2/4:
	print "NO"
else:
	vow = set(perm(["i","a","a","e","u","u"]))
	con = perm(["n","b","m","g","r"])
	for v in vow:
		for c in con:
			vc = [p[0]+p[1] for p in zip(c,v)] + [v[5]]
			for nl in perm(vc):
				name = "".join(nl)
				if name not in used:
					print name
					quit()
	print "NO"