diff = set(chr(ord("a") + i) for i in range(26)) - set(input().rstrip("\n"))



print(((list(sorted(diff))+["None"])[0]))
[print(un_appearence[0] if un_appearence else "None") for un_appearence in [[chr(i) for i in range(ord('a'), ord('z') + 1) if chr(i) not in string] for string in [input()]]]

diff = set(chr(ord("a") + i) for i in range(26)) - set(input().rstrip("\n"))
print(((list(sorted(diff)) + ["None"])[0]))

[
    print(un_appearence[0] if un_appearence else "None")
    for un_appearence in [
        [chr(i) for i in range(ord("a"), ord("z") + 1) if chr(i) not in string]
        for string in [input()]
    ]
]

-diff = set(chr(ord("a") + i) for i in range(26)) - set(input().rstrip("\n")) -print(((list(sorted(diff)) + ["None"])[0])) +[ +    print(un_appearence[0] if un_appearence else "None") +    for un_appearence in [ +        [chr(i) for i in range(ord("a"), ord("z") + 1) if chr(i) not in string] +        for string in [input()] +    ] +]