strings = list(eval(input()))

alfabet  = 'abcdefghijklmnopqrstuvwxyz'



for i in alfabet:

    if strings.count(i) == 0:

        result = i

        break

else:

    result = "None"



print(result)
S = sorted(set([i for i in eval(input())]))

for i in "abcdefghijklmnopqrstuvwxyz":

    if i not in S:

        print(i)

        break

else:print("None")
strings = list(eval(input()))
alfabet = "abcdefghijklmnopqrstuvwxyz"
for i in alfabet:
    if strings.count(i) == 0:
        result = i
        break
else:
    result = "None"
print(result)

S = sorted(set([i for i in eval(input())]))
for i in "abcdefghijklmnopqrstuvwxyz":
    if i not in S:
        print(i)
        break
else:
    print("None")

-strings = list(eval(input())) -alfabet = "abcdefghijklmnopqrstuvwxyz" -for i in alfabet: -    if strings.count(i) == 0: -        result = i +S = sorted(set([i for i in eval(input())])) +for i in "abcdefghijklmnopqrstuvwxyz": +    if i not in S: +        print(i) -    result = "None" -print(result) +    print("None")