s = eval(input())

bkt = [0 for _ in range(26)]

for i in range(len(s)):

    bkt[ord(s[i])-97] = 1

print(('None' if sum(bkt) == 26 else chr(bkt.index(0) + 97)))
S = set(eval(input()))

for i in range(97, 123):

    c = chr(i)

    if c not in S:

        print(c)

        exit()

print('None')
s = eval(input())
bkt = [0 for _ in range(26)]
for i in range(len(s)):
    bkt[ord(s[i]) - 97] = 1
print(("None" if sum(bkt) == 26 else chr(bkt.index(0) + 97)))

S = set(eval(input()))
for i in range(97, 123):
    c = chr(i)
    if c not in S:
        print(c)
        exit()
print("None")

-s = eval(input()) -bkt = [0 for _ in range(26)] -for i in range(len(s)): -    bkt[ord(s[i]) - 97] = 1 -print(("None" if sum(bkt) == 26 else chr(bkt.index(0) + 97))) +S = set(eval(input())) +for i in range(97, 123): +    c = chr(i) +    if c not in S: +        print(c) +        exit() +print("None")