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())
USED = [False] * 26

for s in S:
  USED[ord(s)-97] = True
  
ok = False
ans = None
for i in range(26):
  if not USED[i]:
    ans = chr(97+i)
    ok = True
    break
    
if ok:
  print(ans)
else:
  print("None")

Submission status: Accepted

Solution code:
S = list(input())
chars = [chr(ord('a')+i) for i in range(26)]
for i in chars:
    if i not in S:
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
T = input()
L = [chr(l) for l in range(ord("a"), ord("z")+1)]
L = [l for l in L if l not in T]
print(min(L) if len(L)>0 else "None")

Submission status: Accepted

Solution code:
S = input()
l = len(S)
mozi = []
for i in range(l):
    mozi.append(S[i])
mozi = list(set(mozi))
C = [chr(i) for i in range(ord("a"),ord("z")+1)]

for i in mozi:
    for j in C:
        if i == j:
            C.remove(j)
if len(C) == 0:
    print("None")
else:
    print(C[0])

Submission status: Accepted

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

Submission status: Accepted

Solution code:
s = 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(s)) :
    if s[i] in alpha :
        alpha.remove(s[i])
if alpha :
    print(alpha[0])
else :
    print("None")

Submission status: Accepted

Solution code:
S = input()
a = [s for s in "abcdefghijklmnopqrstuvwxyz"]

for s in list(set(S)):
    if(s in a):
        a.remove(s)
if(a == []):
    print("None")
else:
    print(a[0])

Submission status: Accepted

Solution code:
s = set(input())
al = set(list(map(chr, [i for i in range(97, 97+26)])))
print('None' if len(s)==len(al) else min(al-s))

Submission status: Accepted

Solution code:
from sys import exit

s = input()

for i in range(ord('a'), ord('z')+1):
    if chr(i) not in s:
        print(chr(i))
        exit()

print('None')

Submission status: Accepted

Solution code:
import sys
s = input()
for one in range(97,97+26):
    c = chr(one)
    if not c in s:
        print(c)
        sys.exit()
print("None")

Submission status: Accepted

Solution code:
s_set = set(input())
ord_a = ord("a")
ans = "None"
for i in range(26):
    c = chr(ord_a + i)
    if c not in s_set:
        ans = c
        break
print(ans)

Submission status: Accepted

Solution code:
N=list(input())
s=set(N)
ans=''.join(sorted(s))
all=[chr(i) for i in range(97,97+26)]
if ans=='abcdefghijklmnopqrstuvwxyz':
  print('None')
  exit()
for i in range(len(ans)):
  if ans[i]!=all[i]:
    print(all[i])
    exit()
  elif i==len(ans)-1 :
    print(all[len(ans)])
    exit()

Submission status: Accepted

Solution code:
import sys

S = set(input())
alpha = [chr(i) for i in range(ord('a'), ord('z')+1)]
for i in alpha:
    if not i in S:
        print(i)
        sys.exit()
print('None')

Submission status: Accepted

Solution code:
S = input()

appeared = [False] * 26
for c in S:
    appeared[ord(c) - ord('a')] = True

for i in range(26):
    if not appeared[i]:
        print(chr(ord('a') + i))
        exit(0)

print("None")

Submission status: Accepted

Solution code:
s = input()

words = [True]*26
for i in range(len(s)):
  words[ord(s[i])-97] = False
for i in range(26):
  if words[i]:
    print(chr(i+97))
    exit()
print(None)

Submission status: Accepted

Solution code:
import sys
S = list(input())
D = ['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 d in D:
    if not d in S:
        print(d)
        sys.exit()
print('None')

Submission status: Accepted

Solution code:
import sys
S = input()
C = [False] * 26
for s in S:
    C[ord(s) - ord('a')] = True
for i in range(26):
    if not C[i]:
        print(chr(i + ord('a')))
        sys.exit()
print('None')

Submission status: Accepted

Solution code:
s = set(list(input()))
n = set(list(map(chr,list(range(97,97+26)))))
print('None' if len(s)==len(n) else min(n-s))

Submission status: Accepted

Solution code:
import string

s = input()

t = string.ascii_lowercase

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

print("None")

Submission status: Accepted

Solution code:
#!/usr/bin/env python3
a = [0] * 26
s = input()
for i in s:
    a[ord(i) - 97] = 1
print('None'*(sum(a)==26) or chr(a.index(0) + 97))

Submission status: Accepted

Solution code:
s=input()
ans='None'
dic='abcdefghijklnmopqrstuvwxyz'
for i in range(26):
    if dic[i] not in s:
        ans=dic[i]
        break
print(ans)

Submission status: Accepted

Solution code:
A="abcdefghijklmnopqrstuvwxyz"
S=input()
S=sorted(set(S))

for i in range(len(S)):
	if S[i]!=A[i]:
		print(A[i])
		exit()
if len(S)<len(A):
	print(A[len(S)])
	exit()
print("None")

Submission status: Accepted

Solution code:
alp='abcdefghijklmnopqrstuvwxyz'
S=input()
a=[0 for i in range(26)]
for s in S:
    a[alp.index(s)]+=1
if a.count(0)>=1:
    print(alp[a.index(0)])
else:
    print("None")

Submission status: Accepted

Solution code:
import string
import sys
s = str(input())
low = string.ascii_lowercase
fin = ''
for i in range(len(low)):
    if low[i] not in s:
        print(low[i])
        sys.exit()
print('None')

Submission status: Accepted

Solution code:
import string
s = str(input())
low = string.ascii_lowercase
fin = ''
for i in range(len(low)):
    if low[i] not in s:
        fin += low[i]
if len(fin) == 0:
    print('None')
else:
    print(fin[0])

Submission status: Accepted

Solution code:
S = input()

for n in range(97,123):
  if chr(n) not in S:
    print(chr(n))
    exit()

print("None")

Submission status: Accepted

Solution code:
S = input()
L = [chr(i) for i in range(ord('a'), ord('z')+1)]

for l in L:
    if l not in S:
        print(l)
        exit(0)

print("None")

Submission status: Accepted

Solution code:
S = sorted(list(set(list(input()))))
alfabet = ["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"]
count = 0
for char in alfabet:
    if not(char in S):
        print(char)
        break
    count+=1
if count == 26:
    print("None")

Submission status: Accepted

Solution code:
#!/usr/bin/env python3
arr = [chr(i) for i in range(97, 97+26)]
s = set([c for c in input()])

for c in arr:
    if not (c in s):
        print(c)
        break
else:
    print("None")

Submission status: Accepted

Solution code:
import sys
input=sys.stdin.readline

alp=[chr(i) for i in range(97, 97+26)]
s=input().rstrip()

for i in alp:
    if not i in s:
        print(i)
        exit()
print(None)

Submission status: Accepted

Solution code:
S = set(input())
for i in range(97, 123):
    c = chr(i)
    if c not in S:
        print(c)
        exit()
print('None')

Submission status: Accepted

Solution code:
s = input()
bkt = [0 for _ in range(26)]
for i in range(len(s)):
    bkt[ord(s[i])-97] = 1
print('None' if sum(bkt) == 26 else chr(bkt.index(0) + 97))

Submission status: Accepted

Solution code:
s = input()
alphabet = list(chr(ord("a")+i)for i in range(26))
a = [0]*26

for i in s:
    for j in range(26):
        if i == alphabet[j]:
            a[j] = 1

b = []
for i in range(26):
    if a[i] == 0:
        b.append(alphabet[i])

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

Submission status: Accepted

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

Submission status: Accepted

Solution code:
alp = 'abcdefghijklmnopqrstuvwxyz'

d = {c:False for c in alp}

s = open(0).read().rstrip()

for c in list(s):
    d[c] = True

isnone = True
for c,b in d.items():
    if not b:
        isnone = False
        print(c)
        break
if isnone:
    print('None')

Submission status: Accepted

Solution code:
S = input()
S = sorted(S)
alpha = [chr(i)for i in range(97,97+26)]
ans = "None"
for W in alpha:
    if not(W in S):
        ans = W
        break
print(ans)

Submission status: Accepted

Solution code:
s=input()
A=[False]*26
for i in range(len(s)):
    A[ord(s[i])-97]=True
for i in range(26):
    if A[i]==False:
        print(chr(i+97))
        break
else:
    print("None")

Submission status: Accepted

Solution code:
s = input()

dic = "abcdefghijklmnopqrstuvwxyz"
nf = sorted(set(dic) - set(s))
ans = nf[0] if len(nf) > 0 else "None"

print(ans)

Submission status: Accepted

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

S = list(str(input()))

chr_ord = 97

for i in range(26):
    if chr(chr_ord + i) not in S:
        print(chr(chr_ord + i))
        exit()

print('None')

Submission status: Accepted

Solution code:
S = sorted(list(input()))
alphabe = list('abcdefghijklmnopqrstuvwxyz')

for s in alphabe:
    if s in S:
        continue
    else:
        ans = s
        break
else:
    ans = 'None'
    
print(ans)

Submission status: Accepted

Solution code:
#!/usr/bin/env python3
# encoding:utf-8
import copy
import random
import bisect #bisect_left　これで二部探索の大小検索が行える
import fractions #最小公倍数などはこっち
import math
import sys
import collections
from decimal import Decimal # 10進数で考慮できる

mod = 10**9+7
sys.setrecursionlimit(mod) # 再帰回数上限はでdefault1000

d = collections.deque()
def LI(): return list(map(int, sys.stdin.readline().split()))

S = str(input())
al = list("abcdefghijklmnopqrstuvwxyz")

for i in al:
    if i in S:
        pass
    else:
        print(i)
        break
else:
    print("None")

Submission status: Accepted

Solution code:
s=input()
count=0
for i in range(97,97+26):
    if chr(i) not in s:
        print(chr(i))
        count+=1
        break
    
if count==0:
    print("None")

Submission status: Accepted

Solution code:
S = input()
alpha = [chr(ord('a') + i) for i in range(26)]

for letter in alpha:
  if not letter in S:
    print(letter)
    exit()
print('None')

Submission status: Accepted

Solution code:
S = list(input())
lst = [chr(i) for i in range(97, 97+26)]
res = sorted(list(set(lst) - set(S)))

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

Submission status: Accepted

Solution code:
s = input()

alphabet_list = ['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(s)):
  if s[i] in alphabet_list:
    try:
      alphabet_list.remove(s[i])
    except ValueError:
      continue

if alphabet_list:
  print(alphabet_list[0])
else:
  print('None')

Submission status: Accepted

Solution code:
s = input()

b = [True] * 26
for c in s:
    b[ord(c) - ord('a')] = False

ans = 'None'
for i in range(26):
    if b[i]:
        ans = chr(ord('a') + i)
        break
print(ans)

Submission status: Accepted

Solution code:
s = input()
s = sorted(s)
s = set(s)
alpha = 'a'
flg = 0
for i in range(1,27):
    if (alpha not in s):
        flg = 1
        break
    else : alpha = chr(ord(alpha)+1)
if (flg): print(alpha)
else: print("None")

Submission status: Accepted

Solution code:
import string
a=string.ascii_lowercase

S=list(input())

for i in range(26):
    if a[i] not in S:
        ans=a[i]
        break
    if i==25:
        ans="None"
print(ans)

Submission status: Accepted

Solution code:
S = input()
s_list = [i for i in S]


eng_list = ['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']

dif = set(eng_list) - set(s_list)
if list(dif) == []:
    print('None')
else:print(sorted(list(dif))[0])

Submission status: Accepted

Solution code:
s = input()

words = [True]*26
for i in range(len(s)):
  words[ord(s[i])-97] = False

for i in range(26):
  if words[i]:
    print(chr(97+i))
    exit()
print(None)

Submission status: Accepted

Solution code:
def resolve():
    s = input()
    al = []
    for i in range(26):
        al.append(False)
    
    for c in s:
        ord_c = ord(c) - ord('a')
        al[ord_c] = True
    
    for i in range(26):
        if al[i] == False:
            print(chr(ord('a') + i))
            break
        if i == 25 and al[i] == True:
            print("None")
resolve()

Submission status: Accepted

Solution code:
s = input()
s = set(s)
abc = "abcdefghijklmnopqrstuvwxyz"
for i in abc:
  if i not in s:
    print(i)
    break
else:
  print("None")

Submission status: Accepted

Solution code:
import collections

s = input()
c = collections.Counter(s)

for i in range(26):
    alpha = chr(i + ord("a"))
    if c[alpha] == 0:
        print(alpha)
        break
else:
    print("None")

Submission status: Accepted

Solution code:
S=input()

U=set([chr(ord("a")+k) for k in range(26)])
T=set()
for s in S:
    T.add(s)

V=list(U-T)
V.sort()

if V:
    print(V[0])
else:
    print("None")

Submission status: Accepted

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

Submission status: Accepted

Solution code:
S = sorted(set(input()))
A = 'abcdefghijklmnopqrstuvwxyz'

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

Submission status: Accepted

Solution code:
s=input()
alp="abcdefghijklmnopqrstuvwxyz"
ans="None"
for i in alp:
  exist=False
  if i in s:
    exist=True
  if not exist:
    ans=i
    break
print(ans)

Submission status: Accepted

Solution code:
import sys

s = sorted(input())
for c in list('abcdefghijklmnopqrstuvwxyz'):
    if not c in s:
        print(c)
        sys.exit()

print('None')

Submission status: Accepted

Solution code:
S = set(input())
base = ord('a')
ans = 'None'
for i in range(26):
    a = chr(base+i)
    if a in S:
        continue
    ans = a
    break
print(ans)

Submission status: Accepted

Solution code:
s=input()
S=[s[i] for i in range(len(s))]
characters=[0 for i in range(97,123)]
len(characters)
for i in range(len(S)):
  characters[ord(S[i])-97]=characters[ord(S[i])-97]+1
if 0 in characters:
  print(chr(characters.index(0)+97))
else:
  print('None')

Submission status: Accepted

Solution code:
# n, m, l = map(int, input().split())

# list_n = list(map(int, input().split()))

# n = input()
# list = [input() for i in range(N)

# list = [[i for i in range(N)] for _ in range(M)]

import sys
import string
input = sys.stdin.readline

S = input()
All_string = list(string.ascii_lowercase)

for i in range(len(S)):
    if S[i] in All_string:
        n = All_string.index(S[i])
        All_string.pop(n)

if not All_string:
    print("None")
else:
    print(All_string[0])

Submission status: Accepted

Solution code:
import sys
s=input()
for i in range(ord("a"),ord("z")+1):
  if chr(i) not in s:
    print(chr(i))
    sys.exit()
print("None")

Submission status: Accepted

Solution code:
s=input()
al="abcdefghijklmnopqrstuvwxyz"
ans=""
d={}
for i in range(int(len(s))):
    if s[i] not in d:
        d[s[i]]=1
for i in range(26):
    if al[i] not in d:
        ans+=al[i]
        print(ans)
        exit()
print("None")

Submission status: Accepted

Solution code:
S = set(list(input()))
char = [chr(ord('a') + i) for i in range(26)]
for c in char:
    if c not in S:
        print(c)
        break
else:
    print('None')

Submission status: Accepted

Solution code:
s=input()
l=[0]*26

for i in range(len(s)):
    l[ord(s[i])-97]=1
i=0
while True:
    if l[i]==0:
        print(chr(i+97))
        break
    else:
        i+=1
    if i==26:
        print('None')
        break

Submission status: Accepted

Solution code:
S = set(list(input()))

A = set(list('abcdefghijklmnopqrstuvwxyz'))

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

Submission status: Accepted

Solution code:
S=input()
dp=[0]*26
for i in S:
  dp[ord(i)-97]=1
for i in range(26):
  if dp[i]==0:
    print(chr(i+97))
    exit()
print('None')

Submission status: Accepted

Solution code:
S = list(input())
S_sort = set(sorted(S))
all_sort = {'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'}
ans = all_sort - S_sort
print('None' if len(ans) == 0  else sorted(list(ans))[0])

Submission status: Accepted

Solution code:
def main():
  s = input()
  flg=0
  for i in range(0,26):
    if chr(ord('a')+i) not in s:
      print(chr(ord('a')+i))
      flg=1
      break
  if flg ==0:
    print("None")
    
main()

Submission status: Accepted

Solution code:
s = input()
for i in range(97, 123):
    if s.find(chr(i)) == -1:
        print(chr(i))
        exit()
    
print('None')

Submission status: Accepted

Solution code:
s = input()
for c in 'abcdefghijklmnopqrstuvwxyz':
    if s.find(c) == -1:
        print(c)
        exit()
    
print('None')

Submission status: Accepted

Solution code:
import collections
import string

s = input()
s_count = collections.Counter(s)
s_list = list(s_count.keys())
ans = []

for alphabet in list(string.ascii_lowercase):
  if not alphabet in s_list:
    ans.append(alphabet)
if ans != []:
  print(ans[0])
else:
  print("None")

Submission status: Accepted

Solution code:
import sys
S = str(input())
if len(S) < 1 or len(S) > 10 ** 5:
    sys.exit()
if not S.islower():
    sys.exit()

array_a_to_z = [chr(ord('a') + i) for i in range(26)]

for I in array_a_to_z:
    if I not in S:
        print(I)
        sys.exit()
print("None")

Submission status: Accepted

Solution code:
arb = 'abcdefghijklmnopqrstuvwxyz'
S = input()
s_S =sorted(set(arb)^set(S))
print('None' if len(s_S) == 0 else s_S[0])

Submission status: Accepted

Solution code:
arb = 'abcdefghijklmnopqrstuvwxyz'
S = input()

ans =''
for i in arb:
    if i not in S:
        ans += i

sort_ans = sorted(ans)
if len(ans)==0:
    print('None')
else:
    print(sort_ans[0])

Submission status: Accepted

Solution code:
s = input()
result = 'None'
for i in range(26):
    if chr(ord('a')+i) not in s:
        result = chr(ord('a')+i)
        break
print(result)

Submission status: Accepted

Solution code:
import sys
s = list(input())
for i in range(0,26):
  if not chr(97+i) in s:
    print(chr(97+i))
    sys.exit()
print("None")

Submission status: Accepted

Solution code:
S = input()

for a in "abcdefghijklmnopqrstuvwxyz":
  if a not in S:
    print(a)
    exit()

print("None")

Submission status: Accepted

Solution code:
s1 = sorted(input())
s2 = "abcdefghijklmnopqrstuvwxyz"

for s in s2:
  if s in s1:
    pass
  else:
    print(s)
    break
else:
  print("None")

Submission status: Accepted

Solution code:
S = input()
alphabet = [chr(i) for i in range(97, 97+26)]

for s in S:
    if s in alphabet:
        alphabet.remove(s)

if alphabet:
    print(alphabet[0])
else:
    print("None")

Submission status: Accepted

Solution code:
S = input().strip()
a = [False]*26
for s in S:
    a[ord(s)-ord('a')] = True

ans = "None"
for i in range(len(a)):
    if not a[i]:
        ans = chr(i+ord('a'))
        break
print(ans)

Submission status: Accepted

Solution code:
s = input()
alphabet = [chr(i) for i in range(97, 97+26)]
tf = True
for i in alphabet:
  if not(i in s):
    print(i)
    tf = False
    break
if tf:
  print('None')

Submission status: Accepted

Solution code:
s = input()
alp = set("abcdefghijklmnopqrstuvwxyz")
print(sorted(list(alp - set(s)))[0] if len(alp - set(s)) != 0 else 'None')

Submission status: Accepted

Solution code:
import collections,sys
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"]
c=collections.Counter(S)
for i in alpha:
    if c[i]==0:
        print(i)
        sys.exit()
print("None")

Submission status: Accepted

Solution code:
def resolve():
    a = "abcdefghijklmnopqrstuvwxyz"
    S = input()
    for ch in a:
        if ch not in S:
            print(ch)
            return
    print("None")

resolve()

Submission status: Accepted

Solution code:
s = str(input())
count = 0
a = 0
for i in range(ord("a"), ord("z")+1):
    if chr(i) in s:
        count += 1
    else:
        a = chr(i)
        break 
print(a if count != 26 else "None")

Submission status: Accepted

Solution code:
s = set(input())
ls = ["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"]
k = 0

for i in range(26):
    alp = ls[i]
    if alp not in s:
        k = 1
        break

if k == 1:
    print(alp)
else:
    print("None")

Submission status: Accepted

Solution code:
import string
s = list(input())
alpha = list(string.ascii_lowercase)
n = len(alpha)
ans = "None"
for i in range(n):
  if alpha[i] not in s:
    ans = alpha[i]
    break

print(ans)

Submission status: Accepted

Solution code:
str = input()

s = 'a'

for i in range(26):
    ord_str = ord(s) + i
    if str.count(chr(ord_str)) == 0:
        print(chr(ord_str))
        break
    elif i == 25:
        print("None")

Submission status: Accepted

Solution code:
#! /usr/bin/env python3

from fractions import gcd
# from math import gcd
from collections import Counter, deque, defaultdict
from heapq import heappush, heappop, heappushpop, heapify, heapreplace, merge
from bisect import bisect_left, bisect_right, bisect, insort_left, insort_right, insort
from itertools import accumulate, product, permutations, combinations, combinations_with_replacement

import string
S = input()

c = Counter(S)

for i in string.ascii_lowercase:
    if(not c[i]):
        print(i)
        exit()
print("None")

Submission status: Accepted

Solution code:
S = list(input())
all = list('abcdefghijklmnopqrstuvwxyz')
ans = sorted(list(set(all) - set(S)))
print(ans[0] if len(ans) != 0 else 'None')

Submission status: Accepted

Solution code:
def i():
	return int(input())
def i2():
	return map(int,input().split())
def s():
	return str(input())
def l():
	return list(input())
def intl():
	return list(int(k) for k in input().split())

s = l()
alf = "abcdefghijklmnopqrstuvwxyz"
for i in range(len(s)):
	alf = alf.replace(s[i],"")
if alf == "":
	print("None")
else:
	print(alf[0])

Submission status: Accepted

Solution code:
def i():
	return int(input())
def i2():
	return map(int,input().split())
def s():
	return str(input())
def l():
	return list(input())
def intl():
	return list(int(k) for k in input().split())

s = l()
alf = "abcdefghijklmnopqrstuvwxyz"
for i in range(len(s)):
	alf = alf.replace(s[i],'')
if alf == "":
	print("None")
else:
	print(alf[0])

Submission status: Accepted

Solution code:
# Vicfred
# https://atcoder.jp/contests/abc071/tasks/abc071_b
# string manipulation, implementation
S = input().strip()
alphabet = "abcdefghijklmnopqrstuvwxyz"

for ch in alphabet:
    if ch not in S:
        print(ch)
        exit()
print("None")

Submission status: Accepted

Solution code:
alphabet = 'abcdefghijklmnopqrstuvwxyz'
s = input()

for i in alphabet:
  if i not in s:
    print(i)
    exit()
print("None")

Submission status: Accepted

Solution code:
s = str(input())
apple = "abcdefghijklmnopqrstuvwxyz"
count = 0
a = 0
for i in apple:
    if i in s:
        count += 1
    else:
        a = i
        break
print(a if count != 26  else "None")

Submission status: Accepted

Solution code:
import string
a = string.ascii_lowercase
S =input()
a = sorted(set(a)^set(S))
if a:
    print(a[0])
else:
    print("None")

Submission status: Accepted

Solution code:
S = input()
lis_S = list(S)

a = "abcdefghijklmnopqrstuvwxyz"

for i in lis_S:
    a = a.replace(i,"")

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

Submission status: Accepted

Solution code:
S = input()
lll = "abcdefghijklmnopqrstuvwxyz"
for i in range(26):
    if lll[i] in S:
        pass
    else:
        print(lll[i])
        exit()
    
print("None")

Submission status: Accepted

Solution code:
S = input()
list_Alpha = list("qwertyuiopasdfghjklzxcvbnm")
list_S = list(S)
for i in list_S:
  if i in list_Alpha:
    list_Alpha.remove(i)
  else:
    continue
if bool(list_Alpha) == True:
  list_Alpha.sort()
  print(list_Alpha[0])
else:
  print("None")

Submission status: Accepted

Solution code:
S=str(input())

import string
alphabet="".join([i for i in string.ascii_lowercase if i not in S])

if(alphabet):
  print(alphabet[0])
else:
  print("None")

Submission status: Accepted

Solution code:
import sys

class alphabet: #Trueなら大文字
    def __init__(self, capitalize):
        self.num = dict() #アルファベットを数字に変換
        self.abc = ["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"]
        if capitalize: 
            for i in range(26): self.abc[i] = self.abc[i].upper()
        for i, a in enumerate(self.abc): self.num[a] = True


def solve():
    S = input()
    AB = alphabet(False)
    for i in range(len(S)):
        AB.num[S[i]] = False
    for a in AB.abc:
        if AB.num[a]:
            print(a)
            break
    else: print("None")

    return 0

if __name__ == "__main__":
    solve()

Submission status: Accepted

Solution code:
s = list(input())
exist = 'abcdefghijklmnopqrstuvwxyz'

j = 0
s = set(s)
s = sorted(s)
if len(s) == 26:
    print('None')
    exit()
for i in range(len(s)+1):
    try:
        if s[i] == exist[j]:
            pass    
        elif s[i] != exist[j]:
            print(exist[j])
            break
        j += 1
    except:
        print('z')

Submission status: Accepted

Solution code:
s = str(input())
a = "abcdefghijklmnopqrstuvwxyz"
count = 0
n = 0
for i in range(len(a)):
    for j in range(len(s)):
        if a[i] == s[j]:
            count += 1
            break
    if count == 0:
        ans = a[i]
        print(ans)
        n = 1
        break
    else:
        count = 0
if n == 0:
    print("None")

Submission status: Accepted

Solution code:
import string
S = set(input())
ascii_lowercase = 'abcdefghijklmnopqrstuvwxyz'
for al in ascii_lowercase:
    if al not in S:
        print(al)
        break
else:
    print('None')

Submission status: Accepted

Solution code:
import string
word=sorted(set((input()))^set(string.ascii_lowercase))
print(word and word[0] or 'None')

Submission status: Accepted

Solution code:
S=input()

if "a" not in S:
    print("a")
elif "b"  not in S:
    print("b")
elif "c"  not in S:
    print("c")
elif "d"  not in S:
    print("d")
elif "e"  not in S:
    print("e")
elif "f"  not in S:
    print("f")
elif "g"  not in S:
    print("g")
elif "h"  not in S:
    print("h")
elif "i"  not in S:
    print("i")
elif "j"  not in S:
    print("j")
elif "k"  not in S:
    print("k")
elif "l"  not in S:
    print("l")
elif "m"  not in S:
    print("m")
elif "n"  not in S:
    print("n")
elif "o"  not in S:
    print("o")
elif "p"  not in S:
    print("p")
elif "q"  not in S:
    print("q")
elif "r"  not in S:
    print("r")
elif "s"  not in S:
    print("s")
elif "t"  not in S:
    print("t")
elif "u"  not in S:
    print("u")
elif "v"  not in S:
    print("v")
elif "w"  not in S:
    print("w")
elif "x"  not in S:
    print("x")
elif "y"  not in S:
    print("y")
elif "z"  not in S:
    print("z")
else:
    print("None")

Submission status: Accepted

Solution code:
#

import sys
input=sys.stdin.readline

def main():
    ab="abcdefghijklmnopqrstuvwxyz"
    S=input()
    ans="None"
    for a in ab:
        if not a in S:
            ans=a
            break
    print(ans)
    
if __name__=="__main__":
    main()

Submission status: Accepted

Solution code:
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']
s = input()
for i in l:
    flag = False
    for aa in s:
        if aa == i:
            flag = True
    if flag == False:
        print(i)
        exit()
print("None")

Submission status: Accepted

Solution code:
#NotFound
s = list(input())
s = set(s)
s = sorted(s)
a = list(str('abcdefghijklmnopqrstuvwyz'))
for i in range(len(s)):
  if s[i] in a:
    a.remove(s[i])
if len(a) == 0:
  print('None')
else:
  print(a[0])

Submission status: Accepted

Solution code:
a=sorted(set(input())^set(chr(i)for i in range(97,123)));print(a and a[0]or None)

Submission status: Accepted

Solution code:
S = set(input())

alphabet = {"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"}

a = alphabet.difference(S)

ans = list(a)
ans.sort()

try:
    print(ans[0])
except:
    print("None")

Submission status: Accepted

Solution code:
s = list(input())
s = set(s)
s = sorted(s)
m = 'abcdefghijklmnopqrstuvwxyz'

for i in range(len(m)):
    if s[i] != m[i]:
        print(m[i])
        exit(0)

    if i + 1 != len(m) and i + 1 == len(s):
        print(m[i + 1])
        exit(0)

print('None')

Submission status: Accepted

Solution code:
s = input()
for i in range(ord('a'), ord('z')+1):
    if chr(i) in s:
        continue
    else:
        print(chr(i))
        break
else:
    print('None')

Submission status: Accepted

Solution code:
S=input()
for i in range(ord("a"),ord("z")+1):
  if chr(i) in S:
    continue
  else:
    print(chr(i))
    exit()
print("None")

Submission status: Accepted

Solution code:
x='abcdefghijklmnopqrstuvwxyz'
xs=set(x)
y=input()
ys=set(y)
d=xs-ys
d=sorted(list(d))
if d==[]:
    print('None')
else:
    print(d[0])

Submission status: Accepted

Solution code:
def resolve():
    S = input()
    abc = "abcdefghijklmnopqrstuvwxyz"
    for i in range(26):
        if S.count(abc[i]) == 0:
            print(abc[i])
            exit()
        else:
            continue
    print("None")
resolve()

Submission status: Accepted

Solution code:
s = input()
letters = set([chr(i) for i in range(97, 97+26)]) - set(s)
if  letters == set():
    print('None')
else:
    print(list(sorted(letters))[0])

Submission status: Accepted

Solution code:
import sys
input = sys.stdin.readline


def read():
    S = input().strip()
    return S,


def solve(S):
    for z in "abcdefghijklmnopqrstuvwxyz":
        if z not in S:
            return z
    return "None"


if __name__ == '__main__':
    inputs = read()
    print(solve(*inputs))

Submission status: Accepted

Solution code:
S = input()
for s in [chr(ord("a")+i) for i in range(26)]:
  if not s in S:
    print(s)
    exit()
    
print("None")

Submission status: Accepted

Solution code:
def searchstring(s) : 
  start = ord('a')
  end = ord('z')
  stringlist = [0] * 256
  for i in range(len(s)) : 
    stringlist[ord(s[i])] += 1
  for i in range(start, end + 1) : 
    if stringlist[i] == 0 : 
      return chr(i)
  return None



s = input()

print(searchstring(s))

Submission status: Accepted

Solution code:
S = input()

al = "abcdefghijklmnopqrstuvwxyz"
for a in al:
    if a not in S:
        print(a)
        break
else:
    print("None")

Submission status: Accepted

Solution code:
S = input()
S = sorted(list(set(S)))

n = 97
for i in range(len(S)):
    if ord(S[i]) == n:
        n += 1
    else:
        break

if n == 123:
    print('None')
else:
    print(chr(n))