L = "".join([chr(i) for i in range(97, 97 + 26)])

for i in list(eval(input())):

    L = L.replace(i, "")

if L == "":

    print("None")

else:

    print((L[0]))

L = "".join([chr(i) for i in range(97, 97 + 26)])

for i in set(list(eval(input()))):

    L = L.replace(i, "")

if L == "":

    print("None")

else:

    print((L[0]))

L = "".join([chr(i) for i in range(97, 97 + 26)])
for i in list(eval(input())):
    L = L.replace(i, "")
if L == "":
    print("None")
else:
    print((L[0]))

L = "".join([chr(i) for i in range(97, 97 + 26)])
for i in set(list(eval(input()))):
    L = L.replace(i, "")
if L == "":
    print("None")
else:
    print((L[0]))

-for i in list(eval(input())): +for i in set(list(eval(input()))):