s = eval(input())

a = "abcdefghijklmnopqrstuvwxyz"



for i in s:

    a = a.replace(i, "")

else:

    if len(a):

        print((a[0]))

    else:

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

a = set("abcdefghijklmnopqrstuvwxyz")

d = a - s

if d:

    print((sorted(d)[0]))

else:

    print("None")
s = eval(input())
a = "abcdefghijklmnopqrstuvwxyz"
for i in s:
    a = a.replace(i, "")
else:
    if len(a):
        print((a[0]))
    else:
        print("None")

s = set(eval(input()))
a = set("abcdefghijklmnopqrstuvwxyz")
d = a - s
if d:
    print((sorted(d)[0]))
else:
    print("None")

-s = eval(input()) -a = "abcdefghijklmnopqrstuvwxyz" -for i in s: -    a = a.replace(i, "") +s = set(eval(input())) +a = set("abcdefghijklmnopqrstuvwxyz") +d = a - s +if d: +    print((sorted(d)[0])) -    if len(a): -        print((a[0])) -    else: -        print("None") +    print("None")