s = eval(input())

alphabets = [0] * 26



for i in s:

    alphabets[ord(i) - ord("a")] += 1



for i in range(26):

    if alphabets[i] == 0:

        print((chr(i + ord("a"))))

        break

else:

    print("None")

s = set(eval(input()))



for i in range(26):

    if chr(i + ord("a")) not in s:

        print((chr(i + ord("a"))))

        break

else:

    print("None")

s = eval(input())
alphabets = [0] * 26
for i in s:
    alphabets[ord(i) - ord("a")] += 1
for i in range(26):
    if alphabets[i] == 0:
        print((chr(i + ord("a"))))
        break
else:
    print("None")

s = set(eval(input()))
for i in range(26):
    if chr(i + ord("a")) not in s:
        print((chr(i + ord("a"))))
        break
else:
    print("None")

-s = eval(input()) -alphabets = [0] * 26 -for i in s: -    alphabets[ord(i) - ord("a")] += 1 +s = set(eval(input())) -    if alphabets[i] == 0: +    if chr(i + ord("a")) not in s: