a=[True]*26

s=eval(input())

for i in range(len(s)):

    a[ord(s[i])-ord("a")]=False

for i in range(26):

    if a[i]:

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

        break

else:

    print("None")
d=[0]*26

for i in eval(input()):

    d[ord(i)-97]+=1

print((chr(97+d.index(0)) if 0 in d else"None"))
a = [True] * 26
s = eval(input())
for i in range(len(s)):
    a[ord(s[i]) - ord("a")] = False
for i in range(26):
    if a[i]:
        print((chr(ord("a") + i)))
        break
else:
    print("None")

d = [0] * 26
for i in eval(input()):
    d[ord(i) - 97] += 1
print((chr(97 + d.index(0)) if 0 in d else "None"))

-a = [True] * 26 -s = eval(input()) -for i in range(len(s)): -    a[ord(s[i]) - ord("a")] = False -for i in range(26): -    if a[i]: -        print((chr(ord("a") + i))) -        break -else: -    print("None") +d = [0] * 26 +for i in eval(input()): +    d[ord(i) - 97] += 1 +print((chr(97 + d.index(0)) if 0 in d else "None"))