s=eval(input())

alph=[chr(i) for i in range(97,97+26)]

for i in s:

    if i in alph:

        alph.remove(i)

if alph:

    print((alph[0]))

else:

    print("None")
s=list(set(eval(input())))

alph=[chr(i) for i in range(97,97+26)]

for i in s:

    if i in alph:

        alph.remove(i)

if alph:

    print((alph[0]))

else:

    print("None")
s = eval(input())
alph = [chr(i) for i in range(97, 97 + 26)]
for i in s:
    if i in alph:
        alph.remove(i)
if alph:
    print((alph[0]))
else:
    print("None")

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

-s = eval(input()) +s = list(set(eval(input())))