s = eval(input())

_s = [a for a in s]

ss = set(_s)



_az = [chr(i) for i in range(ord('a'), ord('z')+1)]

az = set(_az)



diff = list(az - ss)

diff.sort()



if len(diff):

    print((diff[0]))

else:

    print('None')
all_c = 'abcdefghijklmnopqrstuvwxyz'

all_key = set(all_c)



S = set(eval(input()))



dif = all_key - S



_dif = list(dif)

_dif.sort()



if len(_dif):

    print((_dif[0]))

else:

    print('None')

s = eval(input())
_s = [a for a in s]
ss = set(_s)
_az = [chr(i) for i in range(ord("a"), ord("z") + 1)]
az = set(_az)
diff = list(az - ss)
diff.sort()
if len(diff):
    print((diff[0]))
else:
    print("None")

all_c = "abcdefghijklmnopqrstuvwxyz"
all_key = set(all_c)
S = set(eval(input()))
dif = all_key - S
_dif = list(dif)
_dif.sort()
if len(_dif):
    print((_dif[0]))
else:
    print("None")

-s = eval(input()) -_s = [a for a in s] -ss = set(_s) -_az = [chr(i) for i in range(ord("a"), ord("z") + 1)] -az = set(_az) -diff = list(az - ss) -diff.sort() -if len(diff): -    print((diff[0])) +all_c = "abcdefghijklmnopqrstuvwxyz" +all_key = set(all_c) +S = set(eval(input())) +dif = all_key - S +_dif = list(dif) +_dif.sort() +if len(_dif): +    print((_dif[0]))