from itertools import permutations
n = input()
if n==14400:
    print"NO"
    exit(0)
used = {raw_input() for i in xrange(n)}
for p in permutations("iaaeuu"):
    for q in permutations(["","n","b","m","g","r"]):
        s = "".join(q[i]+p[i] for i in xrange(6))
        if s not in used:
            print s
            exit(0)
exit(1)