Problem:


Score : 200 points

Problem Statement

You are given a string S consisting of lowercase English letters.
Find the lexicographically (alphabetically) smallest lowercase English letter that does not occur in S.
If every lowercase English letter occurs in S, print None instead.

Constraints

1 \leq |S| \leq 10^5 (|S| is the length of string S.)

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

Print the lexicographically smallest lowercase English letter that does not occur in S.
If every lowercase English letter occurs in S, print None instead.

Sample Input 1

atcoderregularcontest

Sample Output 1

b

The string atcoderregularcontest contains a, but does not contain b.

Sample Input 2

abcdefghijklmnopqrstuvwxyz

Sample Output 2

None

This string contains every lowercase English letter.

Sample Input 3

fajsonlslfepbjtsaayxbymeskptcumtwrmkkinjxnnucagfrg

Sample Output 3

d



Sample input:
atcoderregularcontest


Sample output:
b

Submission status: Accepted

Solution code:
S=list(input())
alphabet= "abcdefghijklmnopqrstuvwxyz"
flag=True
for i in alphabet:
    if i not in S:
        print(i)
        flag=False
        break
    else:
        continue
if flag==True:
    print("None")
else:
    exit

Submission status: Accepted

Solution code:
s=input()
alphabet=sorted(map(chr,range(97,123)))
print("None" if set(alphabet)==set(list(s)) else sorted(set(alphabet)-set(list(s)))[0])

Submission status: Accepted

Solution code:
alphabet='abcdefghijklmnopqrstuvwxyz'
S=input()
def findabc():
    for i in alphabet:
    	if i not in S:return i
print(findabc())

Submission status: Accepted

Solution code:
from collections import defaultdict
import string

S = input()

letters = defaultdict(lambda: False)
for s in S:
    letters[s] = True

ans = 'None'
for l in string.ascii_lowercase:
    if letters[l] == False:
        ans = l
        break
print(ans)

Submission status: Accepted

Solution code:
import string

s = set(input())
for w in string.ascii_lowercase:
    if w not in s:
        print(w)
        break
else:
    print('None')

Submission status: Accepted

Solution code:
s = list(input())
s.sort()
abc = 'abcdefghijklmnopqrstuvwxyz'
ans = 'None'

for i in range(26):
	if abc[i] in s:
		continue
	else:
		ans = abc[i]
		break
print(ans)

Submission status: Accepted

Solution code:
import itertools
from collections import Counter
import bisect

def main():
    s = list(input())
    s = list(set(s))
    s.sort()
    cur = ord('a')
    # print(s)
    for c in s:
        if cur == ord(c):
            cur = cur + 1
        else:
            print(chr(cur))
            exit()
    if cur == ord('z') + 1:
        print('None')
    else:
        print(chr(cur))

if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
s = sorted(input())
result = ''

for i in range(97, 97+26):
    c = chr(i)
    if c not in s:
        result = c
        break

print(result if result != '' else 'None')

Submission status: Accepted

Solution code:
s = sorted(input())
# lowercase の ascii (a-z) 辞書を生成
dct = {chr(i):0 for i in range(97, 97+26)}
result = ''

for c in s:
    if c in dct:
        dct[c] += 1

for i in range(97, 97+26):
    c = chr(i)
    if c in dct and dct.get(c) == 0:
        result = c
        break

print(result if result != '' else 'None')

Submission status: Accepted

Solution code:
alp = "abcdefghijklmnopqrstuvwxyz"
for c in list(input()):
    alp = alp.replace(c, "")
print(alp[0] if len(alp) else "None")

Submission status: Accepted

Solution code:
s = list(input())
alpha = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
for x in s:
    if x in alpha:
        alpha.remove(x)
print(alpha[0] if len(alpha)>0 else "None")

Submission status: Accepted

Solution code:
import string
S = input()
A = string.ascii_lowercase
ans = list(set(A) - set(S))
ans.sort()
if ans == []:
    print('None')
else:
    print(ans[0])

Submission status: Accepted

Solution code:
s = input()
is_inS = [0] * 26
for c in s:
    is_inS[ord(c) - 97] = 1

for i in range(26):
    if is_inS[i] == 0:
        print(chr(i+97))
        exit()
print("None")

Submission status: Accepted

Solution code:
abc=[chr(i) for i in range(97,97+26)]
s=input()
for i in abc:
    if i not in s:
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
alphabet = {1:"a",2:"b"}
backet = [0]*26
S = input()
for char in S:
    backet[ord(char)-97] = 1
if backet == [1]*26:
    print("None")
else:
    print(chr(backet.index(0)+97))

Submission status: Accepted

Solution code:
import sys
ns = lambda: sys.stdin.readline().rstrip()
ni = lambda: int(ns())
nm = lambda: map(int, sys.stdin.readline().split())
nl = lambda: list(nm())

s = ns()
for i in range(26):
    if chr(i + ord('a')) not in s:
        print(chr(i + ord('a')))
        exit()
print('None')

Submission status: Accepted

Solution code:
s=input()
a=sorted(set(s))
E="abcdefghijklmnopqrstuvwxyz"
if len(set(a))==26:
  print("None")
else:
  count=0
  for i in range(len(a)):
    if a[i]==E[i]:
      count+=1
    else:
      break
  print(E[count])

Submission status: Accepted

Solution code:
S = str(input())
ascii_letters = "abcdefghijklmnopqrstuvwxyz"
for letter in ascii_letters:
    if letter not in S:
        print(letter)
        exit()
print("None")

Submission status: Accepted

Solution code:
S = input()

flag = False
for i in range(97,97 + 26):
    c = chr(i)
    if c not in S:
        print(c)
        flag = True
        break

if not flag:
    print("None")

Submission status: Accepted

Solution code:
S = input().rstrip()
element = [0]*26
for i in range(len(S)):
    s = ord(S[i]) - ord("a")
    element[s] += 1
zero = element.count(0)
print("None" if zero == 0 else chr(ord("a") + element.index(0)))

Submission status: Accepted

Solution code:
s = input()
found = False
at = "X"
for i in 'abcdefghijklmnopqrstuvwxyz':
    if i not in s:
        at = i
        found = True
        break
if found:
    print(at)
else:
    print("None")

Submission status: Accepted

Solution code:
s=list(set(input()))
s.sort()
alpha=[chr(i) for i in range(97, 97+26)]
ans='None'
for i in alpha:
    if i not in s:
        ans=i
        break
print(ans)

Submission status: Accepted

Solution code:
import string
s = str(raw_input())
al = [chr(i) for i in range(97, 97+26)]
opt = list(set(al) - set(list(s)))
opt.sort()
if len(opt) == 0:
	print 'None'
else:
	print opt[0]

Submission status: Accepted

Solution code:
import sys
S = input()

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

setS = sorted(set(S))
for A in alphabets:
  if A not in setS:
    print(A)
    sys.exit()
  else: continue
print('None')

Submission status: Accepted

Solution code:
S=set(input())
for i in range(97,123) :
  if chr(i) in S :
    continue
  else :
    print(chr(i))
    break
else :
  print("None")

Submission status: Accepted

Solution code:
import string

S = list(input())

d = set(list(string.ascii_lowercase[:26])) - set(S)
d = list(d)
d = sorted(d)

if len(d)>0:
    print(d[0])
else:
    print('None')

Submission status: Accepted

Solution code:
s=input()
w=["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]

for x in s:
    if x in w:
       w.remove(x)
if w==[]:
    print("None")
else:
    print(w[0])

Submission status: Accepted

Solution code:
l=[chr(i) for i in range(97,97+26)]
s=list(input())
a=set(l)-set(s)
a=list(a)
a.sort()
if len(a)>0:
  print(a[0])
else:
  print('None')

Submission status: Accepted

Solution code:
#71
s = list(set(input()))
s.sort()
x = list("abcdefghijklmnopqrstuvwxyz")
for i in range(min(len(s),len(x))):
    if s[i] !=x[i]:
        print(x[i])
        break
    if i==25:
        print("None")
        break
    if i+1 == min(len(s),len(x)):
        print(x[i+1])
        break

Submission status: Accepted

Solution code:
s=input()

moji="abcdefghijklmnopqrstuvwxyz"

for i in moji:
  if i not in s:
    print(i)
    break
else:
  print("None")

Submission status: Accepted

Solution code:
s = input()
x=0
listA = ["a","b","c","d","e","f","g","h","i","j","k",
         "l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
for i in range(26):
  if s.count(listA[i])==0:
    print(listA[i])
    x=1
    break
if x==0:
  print("None")

Submission status: Accepted

Solution code:
s = list(set(input()))
d = 'abcdefghijklmnopqrstuvwxyz'
for di in d:
    if di not in s:
        print(di)
        exit()
print('None')

Submission status: Accepted

Solution code:
S = list(input())
str = 'abcdefghijklmnopqrstuvwxyz'
ans = list('abcdefghijklmnopqrstuvwxyz')
for s in str:
  if (s in S):
    ans.remove(s)

ans.sort()
if len(ans) == 0:
  print('None')
else:
  print(ans[0])

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-


S = input()

ans = 'None'
for i in range(26):
    if chr(i + 97) not in S:
        ans = chr(i + 97)
        break

print(ans)

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

A = 'abcdefghijklmnopqrstuvwxyz'

S = input()

for i in A:
    if i not in S:
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

l = []
A = 'abcdefghijklmnopqrstuvwxyz'

S = input()

for i in A:
    if i not in S:
        l.append(i)
print('None' if len(l) == 0 else min(l))

Submission status: Accepted

Solution code:
s = input()
a = list("abcdefghijklmnopqrstuvwxyz")
for i in range(len(a)):
    if s.count(a[i]):
        continue
    else:
        print(a[i])
        exit()
print("None")

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

s = list(input())
t = list("abcdefghijklmnopqrstuvwxyz")

for i in range(len(t)):
    for j in range(len(s)):
        if t[i] == s[j]:
            break
    else:
        print(t[i])
        break
else:
    print("None")

Submission status: Accepted

Solution code:
s=input()
m=[0 for i in range(26)]
for i in range(len(s)):
  m[ord(s[i])-97]=1
a=0
for i in range(26):
  if m[i]==0:
    print(chr(i+97))
    a=1
    break
if a==0:
  print("None")

Submission status: Accepted

Solution code:
import sys

def main():
    input = sys.stdin.readline
    A = list(map(str, input().strip()))
    alph = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
            'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
            'None']

    for a in alph:
        if a not in A:
            return a


if __name__ == '__main__':
    print(main())

Submission status: Accepted

Solution code:
s = list(input())
s = set(s)
alphabet = list("abcdefghijklmnopqrstuvwxyz")
alphabet = set(alphabet)
d = alphabet - s
d = sorted(list(d))
if len(d) > 0:
    print(d[0])
else:
    print("None")

Submission status: Accepted

Solution code:
hoge=input()
flag=0
if(flag==0 and hoge.count("a")==0):
  print("a")
  flag=1

if(flag==0 and hoge.count("b")==0):
  print("b")
  flag=1

if(flag==0 and hoge.count("c")==0):
  print("c")
  flag=1

if(flag==0 and hoge.count("d")==0):
  print("d")
  flag=1

if(flag==0 and hoge.count("e")==0):
  print("e")
  flag=1

if(flag==0 and hoge.count("f")==0):
  print("f")
  flag=1

if(flag==0 and hoge.count("g")==0):
  print("g")
  flag=1

if(flag==0 and hoge.count("h")==0):
  print("h")
  flag=1

if(flag==0 and hoge.count("i")==0):
  print("i")
  flag=1

if(flag==0 and hoge.count("j")==0):
  print("j")
  flag=1

if(flag==0 and hoge.count("k")==0):
  print("k")
  flag=1

if(flag==0 and hoge.count("l")==0):
  print("l")
  flag=1

if(flag==0 and hoge.count("m")==0):
  print("m")
  flag=1

if(flag==0 and hoge.count("n")==0):
  print("n")
  flag=1

if(flag==0 and hoge.count("o")==0):
  print("o")
  flag=1

if(flag==0 and hoge.count("p")==0):
  print("p")
  flag=1

if(flag==0 and hoge.count("q")==0):
  print("q")
  flag=1

if(flag==0 and hoge.count("r")==0):
  print("r")
  flag=1

if(flag==0 and hoge.count("s")==0):
  print("s")
  flag=1

if(flag==0 and hoge.count("t")==0):
  print("t")
  flag=1

if(flag==0 and hoge.count("u")==0):
  print("u")
  flag=1

if(flag==0 and hoge.count("v")==0):
  print("v")
  flag=1

if(flag==0 and hoge.count("w")==0):
  print("w")
  flag=1

if(flag==0 and hoge.count("x")==0):
  print("x")
  flag=1

if(flag==0 and hoge.count("y")==0):
  print("y")
  flag=1

if(flag==0 and hoge.count("z")==0):
  print("z")
  flag=1
  
if(flag==0):
  print("None")

Submission status: Accepted

Solution code:
S = input()
Slist = []
for i in range(len(S)):
    Slist.append(ord(S[i]))
Slist = set(Slist)
i = 97
while i < 123:
    if i in Slist:
        i += 1
    else:
        print(chr(i))
        break
if i == 123:
    print('None')

Submission status: Accepted

Solution code:
S = input()

Ans = "None"
for i in range(26):
    if chr(i+97) not in S:
        Ans = chr(i+97)
        break

print(Ans)

Submission status: Accepted

Solution code:
s=input()
for i in range(97,123):
  if chr(i) in s:
    continue
  else:
    print(chr(i))
    break
else:
  print("None")

Submission status: Accepted

Solution code:
al="abcdefghijklmnopqrstuvwxyz"
s=input()
for i in al:
    if not i in s:
        print(i)
        break
    if i=='z':
        print('None')

Submission status: Accepted

Solution code:
s = input()

for i in range(ord('a'), ord('a')+26):
    if not chr(i) in s:
        print(chr(i))
        break
else:
    print('None')

Submission status: Accepted

Solution code:
S = list(input())
alphabet = list('abcdefghijklmnopqrstuvwxyz')
bucket = {}
for a in alphabet:
  bucket[a] = 0
for s in S:
  bucket[s] += 1
for a in alphabet:
  if bucket[a] == 0:
    print(a)
    break
else:
    print('None')

Submission status: Accepted

Solution code:
S = set(input())
result = list(set([chr(i) for i in range(97, 97+26)]) - S)
result.sort()
if result == []:
  print('None')
else:
  print(result[0])

Submission status: Accepted

Solution code:
s = str(input())
     
alphabet = "abcdefghijklmnopqrstuvwxyz"
     
ans ='None' 
for i in range(len(alphabet)):
        if not alphabet[i] in s:
                ans = alphabet[i]
                break
print(ans)

Submission status: Accepted

Solution code:
S = input()

an = ord("a")
cs = [False] * 26
for s in S:
    sn = ord(s)
    cs[sn-an] = True
    
for i, c in enumerate(cs):
    if not c:
        print(chr(i+an))
        break
else:
    print("None")

Submission status: Accepted

Solution code:
# 071 B 
#http://hetapy.hatenablog.com/entry/2013/08/23/115537
# lower-case a-z
alp = [chr(i) for i in range(97,97+26)]
S = input()
l = list()
for i in S:
    l.append(i)
L =list(set(alp) - set(l))
if len(L)==0:
    print("None")
    exit()
L.sort()
print(L[0])

Submission status: Accepted

Solution code:
s=input()
alpha='abcdefghijklmnopqrstuvwxyz'
from collections import defaultdict
d=defaultdict(int)
for i in s:
    d[i]+=1
ans='None'
for a in alpha:
    if d[a]==0:
        ans=a
        break
print(ans)

Submission status: Accepted

Solution code:
abc_list = [chr(i) for i in range(97,97+26)]
input_list = list(input())
p_flag = 0
for i in abc_list:
    try:
        input_list.remove(i)
    except:
        print(i)
        p_flag = 1
        break
if(p_flag == 0):
    print("None")

Submission status: Accepted

Solution code:
a = 'abcdefghijklnmopqrstuvwxyz'

S = input()
for i in a:
    if i not in S:
        print(i)
        exit(0)
print('None')

Submission status: Accepted

Solution code:
s,d=input(),"abcdefghijklmnopqrstuvwxyz"
for i in range(26):
  if not d[i]in s:
    print(d[i])
    exit()
print("None")

Submission status: Accepted

Solution code:
def not_found(S: str)->str:
    for c in 'abcdefghijklmnopqrstuvwxyz':
        if c not in S:
            return c
    return 'None'


if __name__ == "__main__":
    S = input()
    ans = not_found(S)
    print(ans)

Submission status: Accepted

Solution code:
small=list('abcdefghijklmnopqrstuvwxyz')
s=list(input())
if len(set(s)&set(small))==26:
  print('None')
else:
  q=list(set(s)&set(small))
  for i in small:
    if i in q:
      continue
    else:
      print(i)
      exit()

Submission status: Accepted

Solution code:
s = input()
for i in "abcdefghijklmnopqrstuvwxyz":
    if s.find(i)==-1:
        print(i)
        exit()
else:
    print("None")

Submission status: Accepted

Solution code:
s=input()

L=list(s)

X=[0]*150
for i in L:
    X[ord(i)]+=1

ans='None'
for j in range(97,123):
    if X[j]==0:
        ans=chr(j)
        break

print(ans)

Submission status: Accepted

Solution code:
import string
S = sorted(list(set(input())))
for i, x in enumerate(string.ascii_lowercase):
    if len(S) <= i or S[i] != x:
        print(x)
        exit()
print("None")

Submission status: Accepted

Solution code:
s = list(input())
alphabet_list = [chr(i) for i in range(97,97+26)]
for sl in s:
    if sl in alphabet_list:
        alphabet_list.remove(sl)
    else:
        pass
if len(alphabet_list) == 0:
    print('None')
else:
    print(alphabet_list[0])

Submission status: Accepted

Solution code:
def main():
    S = input()
    alph = [chr(i) for i in range(97, 97 + 26)]
    for _ in alph:
        if _ not in S:
            print(_)
            return
    print("None")

if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
s = {c for c in input()}
for c in "abcdefghijklmnopqrstuvwxyz":
  if c not in s:
    print(c)
    break
else:
  print("None")

Submission status: Accepted

Solution code:
S = str(input())
M = "abcdefghijklmnopqrstuvwxyz"
result = M.strip(S)
char_len = len(result)
if char_len == 0:
        print("None")
else:
        print(result[0])

Submission status: Accepted

Solution code:
s = list(input())

alpha = list('abcdefghijklmnopqrstuvwxyz')
c = 0

for i in range(len(alpha)):
	if alpha[i] not in s:
		print(alpha[i])
		c += 1              
		break
        
if c == 0:
	print('None')

Submission status: Accepted

Solution code:
a = 'abcdefghijklmnopqrstuvwxyz'
s = list(input())
for i in a:
    if i not in s:
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
S = input()
l = [chr(i) for i in range(ord('a'), ord('z')+1) if chr(i) not in S]

if len(l) == 0:
    print("None")
else:
    print(l[0])

Submission status: Accepted

Solution code:
letters=[chr(x) for x in range(97,97+26)]
S=str(input())
for i in range(len(S)):
  if S[i] in letters:
    letters.remove(S[i])
print(letters[0]) if letters else print('None')

Submission status: Accepted

Solution code:
import math

def A():
    x, a, b = [int(x) for x in input().split()]
    if abs(x-a) < abs(x-b):
        print('A')
    else:
        print('B')
def B():
    S = input()
    alphabet = [False for x in range(26)]
    for char in S:
        i = ord(char) - ord('a')
        alphabet[i] = True
    printed = False
    for i in range(len(alphabet)):
        if alphabet[i] == False:
            print(chr(ord('a')+i))
            printed = True
            break
    if printed == False:
        print("None")
def C():
    n = int(input())
    three = 0

B()

Submission status: Accepted

Solution code:
import math

def A():
    x, a, b = [int(x) for x in input().split()]
    if abs(x-a) < abs(x-b):
        print('A')
    else:
        print('B')
def B():
    S = input()
    alphabet = [False for x in range(26)]
    for char in S:
        i = ord(char) - ord('a')
        alphabet[i] = True
    printed = False
    for i in range(len(alphabet)):
        if alphabet[i] == False:
            print(chr(ord('a')+i))
            printed = True
            break
    if printed == False:
        print("None")
B()

Submission status: Accepted

Solution code:
#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
import itertools
sys.setrecursionlimit(10**5)
stdin = sys.stdin
def LI(): return list(map(int, stdin.readline().split()))
def LF(): return list(map(float, stdin.readline().split()))
def LI_(): return list(map(lambda x: int(x)-1, stdin.readline().split()))
def II(): return int(stdin.readline())
def IF(): return float(stdin.readline())
def LS(): return list(map(list, stdin.readline().split()))
def S(): return list(stdin.readline().rstrip())
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
alp = [chr(ord('a') + i) for i in range(26)]
#A
def A():
    x, a, b = LI()
    if abs(x - a) > abs(x - b):
        print("B")
    else:
        print("A")
    return

#B
def B():
    s = S()
    s = set(s)
    for i in s:
        alp.remove(i)
    if len(alp) == 0:
        print("None")
    else:
        print(alp[0])
    return

#C
def C():
    return

#D
def D():
    return

#E
def E():
    return

#F
def F():
    return

#G
def G():
    return

#H
def H():
    return

#Solve
if __name__ == '__main__':
    B()

Submission status: Accepted

Solution code:
#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS():return list(map(list, sys.stdin.readline().split()))
def S(): return list(sys.stdin.readline())[:-1]
def IR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = I()
    return l
def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = LI()
    return l
def SR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = S()
    return l
def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = SR()
    return l
mod = 1000000007

#A
"""
x,a,b = LI()
if abs(a-x) < abs(b-x):
    print("A")
else:
    print("B")
"""
#B
s = S()
alp = list("qwertyuiopasdfghjklzxcvbnm")
alp.sort()
d = defaultdict(int)
for i in alp:
    d[i] += 1
for i in s:
    d[i] -= 1
for i in d.keys():
    if d[i] > 0:
        print(i)
        quit()
print("None")
#C
"""
n = I()
d = defaultdict(int)
a = LI()
for i in a:
    d[i] += 1
d = list(d.items())
d.sort(key = lambda x:-x[0])
l = 0
k = 0
for i,j in d:
    if j >= 2:
        if l == 0:
            l = i
        else:
            k = i
        if j >= 4:
            k = i
    if k != 0:break
print(l*k)
"""

#D
"""
n = I()
s1 = S()
s2 = S()
ans = 0
i = 0
key = 1
d = defaultdict(int)
while i < n:
    if s1[i] == s2[i]:
        if not d[s1[i]]:
            d[s1[i]] = 1
            if i == 0:
                ans = 3
            else:
                if key:
                    ans *= 2
        key = 1
    else:
        if not d[s1[i]] and not d[s2[i]]:
            d[s1[i]] = 1
            d[s2[i]] = 1
            if i == 0:
                ans = 6
            else:
                if key:
                    ans *= 2
                else:
                    ans *= 3
        if not d[s1[i]]:
            d[s1[i]] = 1
            if not key:
                ans *= 2
        if not d[s2[i]]:
            d[s2[i]] = 1
            if not key:
                ans *= 2
        key = 0
        i += 1
    i += 1
    ans %= mod
print(ans)
"""

#E

#F

#G

#H

#I

#J

#K

#L

#M

#N

#O

#P

#Q

#R

#S

#T

Submission status: Accepted

Solution code:
a=[True]*26
s=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")

Submission status: Accepted

Solution code:
S=str(input())
p=0
L=['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']
for i in range(26):
    check=L[i] in S
    if check==True:
        p+=1
    else:
        print(L[i])
        break
if p==26:
    print('None')

Submission status: Accepted

Solution code:
S = set(list(input()))
alpha = set([chr(ord('a') + i) for i in range(26)])
answer = alpha - S
L=list(answer)
if len(L) == 0:
    print('None')
else:
    L.sort()
    print(L[0])

Submission status: Accepted

Solution code:
S = list(set(input()))
alpha = "abcdefghijklnmopqrstuvwxyz"
S.sort
for i in range(len(alpha)):
    if alpha[i] not in S:
        print(alpha[i])
        exit()
print('None')

Submission status: Accepted

Solution code:
s = input()

for i in [chr(i) for i in range(97, 97+26)]:
    if s.count(i) == 0:
        print(i)
        exit()

print("None")

Submission status: Accepted

Solution code:
s = set("abcdefghijklmnopqrstuvwxyz").difference(set(input()))
if len(s) == 0:
  print("None")
else:
  print(min(s))

Submission status: Accepted

Solution code:
alfa = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
S = [i for i in input()]
for s in set(S):
    if s in alfa:
        alfa.remove(s)
if len(alfa)==0:
    print("None")
else:
    print(alfa[0])

Submission status: Accepted

Solution code:
S = input()

ans = None
for i in range(26):
    c = chr(i + ord('a'))
    if not c in S:
        ans = c
        break

print("None" if ans is None else ans)

Submission status: Accepted

Solution code:
print(min(set(map(chr,range(97,123)))-set(input())or["None"]))
#char型a~zのセットから入力分引いた残りの最小値 なければ"None"

Submission status: Accepted

Solution code:
S = set(input())
judge = True
albet=list("abcdefghijklmnopqrstuvwxyz")
for i in range(26):
    if not(albet[i] in S):
        judge = False
        break
        

if judge:
    print("None")
else:
    print(albet[i])

Submission status: Accepted

Solution code:
S = list(set(input()))
S.sort()
tmp = "abcdefghijklmnopqrstuvwxyz"
for i in range(0,len(tmp),1):
    if tmp[i] not in S:
        print(tmp[i])
        exit()
print("None")

Submission status: Accepted

Solution code:
S = input()

alphabet = "abcdefghijklmnopqrstuvwxyz"

for alp in alphabet:
    if alp not in S:
        print(alp)
        break
else:
    print("None")

Submission status: Accepted

Solution code:
S = input()
ans = "abcdefghijklmnopqrstuvwxyz"
for s in S:
  ans = ans.replace(s, "")
if(ans == ""):
  print("None")
else:
  print(ans[0])

Submission status: Accepted

Solution code:
def main():
    S = input()
    memo = [True] * 26
    a = ord('a')
    for c in S:
        memo[ord(c) - a] = False
    for i in range(26):
        if memo[i]:
            print(chr(i+a))
            return
    print("None")


if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
a = set(list(input()))
ans = "None"
for i in range(ord("a"),ord("z")+1):
  if not chr(i) in a:
    ans = chr(i)
    break
print(ans)

Submission status: Accepted

Solution code:
s = input()

u = set(s)

if len(u) == 26:
	print("None")
	exit()
	
al = set("abcdefghijklmnopqrstuvwxyz")

print(sorted(al - u)[0])

Submission status: Accepted

Solution code:
tester = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
s = input()

for i in tester:
    if i not in s:
        print(i)
        exit()

print("None")

Submission status: Accepted

Solution code:
s = list(input())

alph = [chr(i) for i in range(97, 97+26)]
l = list(set(alph) - set(s))
l.sort()
print(l[0]) if l != [] else print("None")

Submission status: Accepted

Solution code:
al = 'abcdefghijklmnopqrstuvwxyz'
s = input()
s = ''.join(sorted(list(set(s))))
for a in al:
  if a not in s:
    print(a)
    break
else:
  print('None')

Submission status: Accepted

Solution code:
al = 'abcdefghijklmnopqrstuvwxyz'
s = input()
s = ''.join(sorted(list(set(s))))
for a in al:
  if a not in s:
    print(a)
    break
else:
  print('None')

Submission status: Accepted

Solution code:
S = input()

isAppeared = [False]*(26)

for s in S:
    for i in range(97, 97+26):
        if s == chr( i ): isAppeared[i-97] = True

def printLetter( isAppeared ):
    for i in range(26):
        if isAppeared[i] == False:
            print( chr(i+97) )
            return
    print( 'None' )

printLetter( isAppeared )

Submission status: Accepted

Solution code:
s = input()
words = 'abcdefghijklmnopqrstuvwxyz'
for i in words:
    if i not in s:
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
s=input()
a="qwertyuioplkjhgfdsazxcvbnm"
kouho=[]
for i in a:
    if i not in s:kouho.append(i)
kouho=sorted(kouho)
print(kouho[0]) if len(kouho)!=0 else print("None")

Submission status: Accepted

Solution code:
"""AtCoder"""

S = input()

word = "abcdefghijklnmopqrstuvwxyz"

S = list(set(S))

S.sort()

for i in range(len(word)):
    if word[i] not in S:
        print(word[i])
        exit()

print("None")

Submission status: Accepted

Solution code:
# python template for atcoder1
import sys
sys.setrecursionlimit(10**9)
input = sys.stdin.readline
s = input()
alpha = [chr(i) for i in range(97, 97+26)]
for c in alpha:
    if c in s:
        continue
    else:
        print(c)
        exit()
print("None")

Submission status: Accepted

Solution code:
S = list(input())
S = set(S)
S = list(S)
S.sort()
alphabet = list('abcdefghijklmnopqrstuvwxyz')

if(len(S) == 26):
  print('None')
else:
 for i in range(len(S)):
   alphabet.remove(S[i])
 print(alphabet[0])

Submission status: Accepted

Solution code:
import cmath
import numpy as np
import sys

INF=1e18
MOD=1e9+7

s=input()

alp = "abcdefghijklmnopqrstuvwxyz"

for c in alp:
    if c not in s:
        print(c)
        sys.exit()

print('None')

Submission status: Accepted

Solution code:
S = list(input())
alpha = ['a','b','c','d','e','f','g','h','i','j','k','l',\
        'm','n','o','p','q','r','s','t','u','v','w','x','y','z']
for i in range(len(alpha)):
    if S.count(alpha[i])==0:
        print(alpha[i])
        exit()
print('None')

Submission status: Accepted

Solution code:
d=set(input())
for c in "abcdefghijklmnopqrstuvwxyz":
  if c not in d:print(c);exit()
print("None")

Submission status: Accepted

Solution code:
s=input()
abc="abcdefghijklmnopqrstuvwxyz"
for i in range(len(abc)):
    if (abc[i] in s)==False:
        print(abc[i])
        break
else:
    print("None")

Submission status: Accepted

Solution code:
# coding: utf-8
S = input()
s = [chr(97 + i) for i in range(26)]
ans = 'None'
for i in s:
    if i not in S:
        ans = i
        break
print(ans)

Submission status: Accepted

Solution code:
s = input()
l = list('abcdefghijklmnopqrstuvwxyz')
for l_ in l:
    if l_ in s:
        continue
    else:
        print(l_)
        exit()
print('None')

Submission status: Accepted

Solution code:
s=list(input())
s=set(s)
s=list(s)
s.sort()
k=0
for i in range(26):
    if ord(s[i])-97!=i:
        if i==0:
            print("a")
            k=1
            break
        print(chr(ord(s[i-1])+1))
        break
    if i==25:
        print("None")
        k=1
        break
    if i==len(s)-1:
        print(chr(ord(s[-1])+1))
        break

Submission status: Accepted

Solution code:
s = sorted(list(input()))
check = "abcdefghijklmnopqrstuvwxyz"

for i in range(26):
    if check[i] not in s:
        print(check[i])
        break
    if i == 25:
        print('None')
        break

Submission status: Accepted

Solution code:
s = str(input())

import string

s = set(sorted(list(s)))
t = set(list(string.ascii_lowercase))
remain = t - s
remain = list(remain)

if len(remain) > 0:
    print(min(remain))
else:
    print('None')

Submission status: Accepted

Solution code:
def notfound(n):
    bucket = {i:False for i in 'abcdefghijklmnopqrstuvwxyz'}
    for i in S:
        bucket[i]=True
    box = [k for k, v in bucket.items() if v == False]
    if box == []:
        return 'None'
    else:
        return sorted(box)[0]
S = input()
print(notfound(S))