S = sorted(eval(input()))

dic = "abcdefghijklmnopqrstuvwxyz"

for s in S:

  if(s in dic):

    dic = dic.replace(s,'')

if(dic != ''):

  print((dic[0]))

else:

  print("None")
S = sorted(set(eval(input())))

dic = "abcdefghijklmnopqrstuvwxyz"

for s in S:

  if(s in dic):

    dic = dic.replace(s,'')

if(dic != ''):

  print((dic[0]))

else:

  print("None")
S = sorted(eval(input()))
dic = "abcdefghijklmnopqrstuvwxyz"
for s in S:
    if s in dic:
        dic = dic.replace(s, "")
if dic != "":
    print((dic[0]))
else:
    print("None")

S = sorted(set(eval(input())))
dic = "abcdefghijklmnopqrstuvwxyz"
for s in S:
    if s in dic:
        dic = dic.replace(s, "")
if dic != "":
    print((dic[0]))
else:
    print("None")

-S = sorted(eval(input())) +S = sorted(set(eval(input())))