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:
from string import ascii_lowercase


S = set(input())
for c in ascii_lowercase:
    if c not in S:
        print(c)
        exit()
print('None')

Submission status: Accepted

Solution code:
s = input()
for i in range(ord('a'), ord('z') + 1):
  c = chr(i)
  if s.count(c) == 0:
    print(c)
    break
else:
  print('None')

Submission status: Accepted

Solution code:
import string
s = set(list(input()))
e = list(string.ascii_lowercase)

for i in e:
    if i in s:
        continue
    else:
        print(i)
        exit()

print("None")

Submission status: Accepted

Solution code:
# Problem:
# Python  Try

import sys
# from collections import defaultdict
# import heapq,copy
# from collections import deque
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

def initSet():
    result = set()
    for j in range(ord('a'),ord('z')+1):
        result.add(chr(j))
    return result

def solver(inputString,allCharSet):
    result = ''
    inputSet = set(inputString)
    # print("INPUT={}".format(inputSet))
    # print("ALL={}".format(allCharSet))
    diffset = allCharSet - inputSet
    # print("DIFF={}".format(diffset))
    difflist = list(diffset)
    difflist.sort()
    # print("{}".format(difflist))
    if len(difflist) == 0:
        result = "None"
    else:
        result = difflist[0]
    return result

if __name__ == "__main__":
    S = sys.stdin.readline().split('\n')
    allset = initSet()
    print("{}".format(solver(S[0],allset)))

Submission status: Accepted

Solution code:
S = input()
alp = [chr(i) for i in range(97, 97 + 26)]
for c in alp:
    if c in S:
        pass
    else:
        print(c)
        break
else:
    print('None')

Submission status: Accepted

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

Submission status: Accepted

Solution code:
s = set(input())

if len(s) == 26:
    print("None")
else:
    print(sorted("".join(set("abcdefghijklmnopqrstuvwxyz") - s))[0])

Submission status: Accepted

Solution code:
list=[chr(i) for i in range(97, 97+26)]
S=input()
S=set(S)
A=[x for x in S]
A=sorted(A)
if len(A)<26:
    A+="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
for i in range(26):
    if A[i] == list[i]:
        pass
    else:
        print(list[i])
        exit()
print("None")

Submission status: Accepted

Solution code:
s=input()
for i in range(97,123):
  if not chr(i) in s:
    print(chr(i))
    break
else:
  print('None')

Submission status: Accepted

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

Submission status: Accepted

Solution code:
s=input()
for i in range(26):
  if s.count(chr(ord('a')+i))==0:
    print(chr(ord('a')+i))
    break
else:
  print('None')

Submission status: Accepted

Solution code:
s=set(input())
a=set([chr(ord('a') + i) for i in range(26)])
b=sorted(s ^ a)
if len(b)!=0:
	print(b[0])
else:
	print('None')

Submission status: Accepted

Solution code:
S=input()
alphabet=[chr(i) for i in range(97,97+26)]
for i in alphabet:
    if i in S:
        continue
    else:
        print(i)
        exit()
print("None")

Submission status: Accepted

Solution code:
from string import ascii_lowercase
S = input()
s = set(S)
for a in ascii_lowercase:
  if a not in s:
    print(a)
    exit()
    
print('None')

Submission status: Accepted

Solution code:
S = input()

al_list = [chr(i) for i in range(97, 97+26)]
s_list = []
Flag = True

for al in S:
    s_list.append(al)

if set(s_list) == set(al_list):
    print('None')
else:
    print(min(list(set(al_list) - set(s_list))))

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','None']

for i in s:
    if i in alpha:
        alpha.remove(i)

print(alpha[0])

Submission status: Accepted

Solution code:
S = input()

for i in range(97,26+97):
    if chr(i) not in S:
        print(chr(i))
        exit(0)
else:
    print('None')

Submission status: Accepted

Solution code:
s = input()

for i in range(97,97+26):
    if chr(i) not in s:
        print(chr(i))
        exit()
print("None")

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-
s = sorted(map(ord, set(input())))
alp = ord('a')

for c in s:
    if c == alp:
        if c == ord('z'):
            print('None')
            quit()
        else:
            alp += 1
            continue
    else:
        print(chr(alp))
        quit()
print(chr(alp))

Submission status: Accepted

Solution code:
s = input()
t = [n for n in range(97,97+26)]
for ss in s:
	tmp = ord(ss)
	if tmp in t:
		t.remove(tmp)
if len(t) > 0:
	print(chr(t[0]))
else:
	print("None")

Submission status: Accepted

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

s = list(s)
a = list(a)

for i in range(0,len(s)):
  if(s[i] in a):
    k = a.index(s[i])
    del a[k]

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

Submission status: Accepted

Solution code:
s = input()
ll = [i for i in range(97,123,1)]
for j in s:
    s_num = ord(j)
    if s_num in ll:
        ll.remove(s_num)
    else:
        pass
if len(ll) != 0:
    print(chr(ll[0]))
else:
    print("None")

Submission status: Accepted

Solution code:
import sys, re
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, tan, asin, acos, atan, radians, degrees, log2
from collections import deque, defaultdict, Counter
from itertools import accumulate, permutations, combinations, combinations_with_replacement, product, groupby
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from fractions import gcd
from heapq import heappush, heappop, heapify
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

S = input()

ans = list(ascii_lowercase)

for x in S:
	if x in ans:
		ans.remove(x)

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

Submission status: Accepted

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

Submission status: Accepted

Solution code:
S=list(input())
l=sorted(list(set(S)))
for (i,j) in zip(range(len(l)),range(97,97+26)):
    if chr(j) !=l[i]:
        print(chr(j))
        exit()
    elif chr(j) == 'z':
        print('None')
        exit()
print(chr(j+1))

Submission status: Accepted

Solution code:
s = input()

for c in range(97,123):
  if not(chr(c) in s):
    print(chr(c))
    break
else:
  print("None")

Submission status: Accepted

Solution code:
S = sorted(set(map(ord, input())))
for c in range(ord('a'), ord('z') + 1):
    if c in S:
        continue
    print(chr(c))
    break
else:
    print('None')

Submission status: Accepted

Solution code:
def instr():
    s = input()
    return(list(s[:len(s)]))


c = "abcdefghijklmnopqrstuvwxyz"
s = instr()

res = "None"
for i in c:
    if i not in s:
        res = i
        break

print(res)

Submission status: Accepted

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

#############
# Libraries #
#############

import sys
input = sys.stdin.readline

import math
#from math import gcd
import bisect
from collections import defaultdict
from collections import deque
from functools import lru_cache


#############
# Constants #
#############

MOD = 10**9+7
INF = float('inf')

#############
# Functions #
#############

######INPUT######
def inputI(): return int(input().strip())
def inputS(): return input().strip()
def inputIL(): return list(map(int,input().split()))
def inputSL(): return list(map(str,input().split()))
def inputILs(n): return list(int(input()) for _ in range(n))
def inputSLs(n): return list(input().strip() for _ in range(n))
def inputILL(n): return [list(map(int, input().split())) for _ in range(n)]
def inputSLL(n): return [list(map(str, input().split())) for _ in range(n)]

######OUTPUT######
def Yes(): print("Yes"); return
def No(): print("No"); return

#####Inverse#####
def inv(n): return pow(n, MOD-2, MOD)

######Combination######
kaijo_memo = []
def kaijo(n):
  if(len(kaijo_memo) > n):
    return kaijo_memo[n]
  if(len(kaijo_memo) == 0):
    kaijo_memo.append(1)
  while(len(kaijo_memo) <= n):
    kaijo_memo.append(kaijo_memo[-1] * len(kaijo_memo) % MOD)
  return kaijo_memo[n]

gyaku_kaijo_memo = []
def gyaku_kaijo(n):
  if(len(gyaku_kaijo_memo) > n):
    return gyaku_kaijo_memo[n]
  if(len(gyaku_kaijo_memo) == 0):
    gyaku_kaijo_memo.append(1)
  while(len(gyaku_kaijo_memo) <= n):
    gyaku_kaijo_memo.append(gyaku_kaijo_memo[-1] * pow(len(gyaku_kaijo_memo),MOD-2,MOD) % MOD)
  return gyaku_kaijo_memo[n]

def nCr(n,r):
  if(n == r):
    return 1
  if(n < r or r < 0):
    return 0
  ret = 1
  ret = ret * kaijo(n) % MOD
  ret = ret * gyaku_kaijo(r) % MOD
  ret = ret * gyaku_kaijo(n-r) % MOD
  return ret

######Factorization######
def factorization(n):
  arr = []
  temp = n
  for i in range(2, int(-(-n**0.5//1))+1):
    if temp%i==0:
      cnt=0
      while temp%i==0: 
        cnt+=1 
        temp //= i
      arr.append([i, cnt])
  if temp!=1:
    arr.append([temp, 1])
  if arr==[]:
    arr.append([n, 1])
  return arr

#####MakeDivisors######
def make_divisors(n):
  divisors = []
  for i in range(1, int(n**0.5)+1):
    if n % i == 0:
      divisors.append(i)
      if i != n // i: 
        divisors.append(n//i)
  return divisors

#####LCM#####
def lcm(a, b):
    return a * b // gcd (a, b)

#####BitCount#####
def count_bit(n):
  count = 0
  while n:
    n &= n -1
    count += 1
  return count

#####ChangeBase#####
def Base_10_to_n(X, n):
  if X//n:
    return Base_10_to_n(X//n, n)+[X%n]
  return [X%n]

def Base_n_to_10(X, n):
  return sum(int(str(X)[-i])*n**i for i in range(len(str(X))))

#####IntLog#####
def int_log(n, a):
  count = 0
  while n>=a:
    n //= a
    count += 1
  return count

#############
# Main Code #
#############
s = inputS()

alpha = "abcdefghijklmnopqrstuvwxyz"

for l in alpha:
  if l not in s:
    print(l)
    exit()
print("None")

Submission status: Accepted

Solution code:
print(min(set(map(chr,range(97,123)))-set(input())or["None"]))

Submission status: Accepted

Solution code:
s=input()
alp="abcdefghijklmnopqrstuvwxyz"
c=0
for i in alp:
    if i not in s:
        print(i)
        c+=1
        break
if c==0:
    print("None")

Submission status: Accepted

Solution code:
from string import ascii_lowercase

S = set(input())

ans = list(set(ascii_lowercase) - S)
ans.sort()
if len(ans):
    print(ans[0])
else:
    print("None")

Submission status: Accepted

Solution code:
S = input()
s = ord("a")

for i in range(26):
  if chr(s) in S:
    s=s+1
    if i==25:
      print("None")
    continue
  else:
    print(chr(s))
    break

Submission status: Accepted

Solution code:
s=input()
ok=True
for i in range(97,97+26):
    if chr(i) not in s:
        ok=False
        print(chr(i))
        break
if ok:
    print("None")

Submission status: Accepted

Solution code:
s = input()

alphabet = 'abcdefghijklmnopqrstuvwxyz'

ans = set(s) ^ set(alphabet)
print(sorted(list(ans))[0]) if len(ans) != 0 else print('None')

Submission status: Accepted

Solution code:
import string
s=input()
non_exists_letters=sorted(list(set(string.ascii_lowercase)-set(s)))
if non_exists_letters:
    print(non_exists_letters[0])
else:
    print('None')

Submission status: Accepted

Solution code:
s = sorted(set(input()))
if len(s)==26:
    print('None')
else:
    for i in range(26):
        if s.count(chr(ord('a')+i))==0:
            print(chr(ord('a')+i))
            break

Submission status: Accepted

Solution code:
S = input()

al = [chr(i) for i in range(ord('a'), ord('z')+1)]

for j in range(len(S)):
    if S[j] in al:
        al.remove(S[j])
if al:
    print(al[0])
else:
    print('None')

Submission status: Accepted

Solution code:
S = list(input())
S = sorted(list(set(S)))
i = 97
for s in S:
    if ord(s) != i:
        print(chr(i))
        exit()
    i += 1
if len(S) < 26:
    print(chr(i))
else:
    print('None')

Submission status: Accepted

Solution code:
S = str(input())
alp = "abcdefghijklmnopqrstuvwxyz"
st = 'None'
for i in range(26):
  if alp[i] not in S:
    st = alp[i]
    break
print(st)

Submission status: Accepted

Solution code:
s = input()
a = 'abcdefghijklmnopqrstuvwxyz'
cnt = []
for i in range(26):
  if a[i] in s:
    continue
  else:
    cnt.append(a[i])
if cnt == []:
    print('None')
else:
    print(cnt[0])

Submission status: Accepted

Solution code:
s = list(input())
s = list(set(s))
for i in range(ord("a"),ord("z")+1):
    if s.count(chr(i)) != 1:
        print(chr(i))
        exit()
print("None")

Submission status: Accepted

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

ans = "None"
for j in [chr(i) for i in range(97,97+26)]:
        if j not in S:
            ans = j
            break

print(ans)

Submission status: Accepted

Solution code:
S = set(list(input()))
L = "abcdefghijklmnopqrstuvwxyz"

ans = "None"
if len(S) != 26:
    for j in L:
        if j not in S:
            ans = j
            break

print(ans)

Submission status: Accepted

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

for t in alphabet:
    if t not in s:
        print(t)
        break
    if t == "z":
        print("None")

Submission status: Accepted

Solution code:
S = list(input())
S = set(S)
ans = "None"
for i in range(26):
  if not(chr(97+i) in S):
    ans = chr(97+i)
    break
print(ans)

Submission status: Accepted

Solution code:
s = input()
for i in range(ord('a'),ord('z')+1):
  if chr(i) not in s:
    print(chr(i))
    break
else:
  print('None')

Submission status: Accepted

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

Submission status: Accepted

Solution code:
S = input()
alphabet_list = [chr(i) for i in range(97, 97 + 26)]
flag = 0
for moji in alphabet_list:
    if moji not in S:
        print(moji)
        flag = 1
        break
if not flag:
    print("None")

Submission status: Accepted

Solution code:
S = input()
S = sorted(set(S))
A = "abcdefghijklmnopqrstuvwxyz"
for i in range(len(A)):
  if len(A) == len(S):
    print("None")
    break
  if A[i] != S[i]:
    print(A[i])
    break
  if i == len(S) - 1:
    print(A[i + 1])
    break

Submission status: Accepted

Solution code:
import sys
S = list(set(list(sys.stdin.readline().strip())))

for s in range(ord('a'), ord('z') + 1):
    if chr(s) not in S:
        print(chr(s))
        exit()
print("None")

Submission status: Accepted

Solution code:
s = list(input())
al=[chr(ord('a') + i) for i in range(26)]

a = list(set(s)^set(al))

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

Submission status: Accepted

Solution code:
from sys import exit

ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

s = input()

sa = sorted(s)
al="abcdefghijklmnopqrstuvwxyz"
cnt=0

for i in range(len(s)):
    if sa[i] == al[cnt]:
        cnt+=1
    if cnt == 26:
        print("None")
        exit()

print(al[cnt])

Submission status: Accepted

Solution code:
S=input()
L=list(set(S))
l=list('abcdefghijklmnopqrstuvwxyz')
for x in L:
  l.remove(x)
  if len(l)==0:
    print('None')
    exit()
else:
  print(l[0])

Submission status: Accepted

Solution code:
s = list(input())
t = ['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(t)):
    if s.count(t[i]) == 0:
        print(t[i])
        exit()
print('None')

Submission status: Accepted

Solution code:
S = list(input())
alphabet = []

for i in range(26):
    alphabet.append(chr(i+97))

x = set(S)

for i in alphabet:
    if i not in x:
        print(i)
        exit()

print('None')

Submission status: Accepted

Solution code:
n=input()

l=[chr(ord('a') + i) for i in range(26)]
for k in l:
    if k not in n:
      print(k)
      exit()
print("None")

Submission status: Accepted

Solution code:
import sys
import math
import bisect

def solve(s):
    for i in range(26):
        c = chr(i + ord('a'))
        if c not in s:
            return c
    return None

def main():
    ans = solve(input())
    if ans:
        print(ans)
    else:
        print('None')

if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
S = list(input())
s = sorted(list(set(S)))
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']

if s == l:
    ans = 'None'
else:
    for i in range(26):
        if (len(s) - 1) < i:
            ans = l[i]
            break
        elif s[i] != l[i]:
            ans = l[i]
            break

print(ans)

Submission status: Accepted

Solution code:
s=str(input())
s=list(s)
s=set(s)
s=list(s)
s.sort()
a="abcdefghijklmnopqrstuvwxyz"
a=list(a)
i=0
count=0
while i<len(s):
  if s[i]!=a[i]:
    print(a[i])
    break
  i=i+1
  count=count+1
else:
  if count==26:
    print("None")
  else:
    print(a[i])

Submission status: Accepted

Solution code:
def main():
    s = input()

    bucket = list('' for _ in range(26))

    for char in s:
        bucket[ord(char) - 97] = char
    
    try:
        print(chr(bucket.index('') + 97))
    except:
        print('None')

if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
# coding: utf-8
S = sorted(input())
A = ['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 A:
    if i not in S:
        print(i)
        exit()
else:
    print('None')

Submission status: Accepted

Solution code:
n=input()

la=[chr(ord('a') + i) for i in range(26)]
for i in la:
    if i not in n:
      print(i)
      exit()
print("None")

Submission status: Accepted

Solution code:
import sys
S = input()
T = []
B = []
A = 'abcdefghijklmnopqrstuvwxyz'
for i in range(len(S)):
   T.append(S[i])
for i in range(len(A)):
   B.append(A[i])
for i in B:
    if not i in T:
        print(i)
        sys.exit()
print('None')

Submission status: Accepted

Solution code:
alp=["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()
l=len(s)

for i in range(l):
    if s[i] in alp:
        alp.remove(s[i])

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

Submission status: Accepted

Solution code:
S = input()
alp = []
for i in range(97,123):
    alp.append(chr(i))
for s in S:
    if s in alp:
        alp.remove(s)
if len(alp) == 0:
    print('None')
else:
    print(alp[0])

Submission status: Accepted

Solution code:
from collections import Counter

s = input()

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

counter = Counter(list(s))

for a in alphabets:
    if counter[a] == 0:
        print(a)
        exit()

print("None")

Submission status: Accepted

Solution code:
import math
def py():
    print("Yes")
def pn():
    print("No")
def iin():
    x = int(input())
    return x

neko = 'None'

s = input()
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']
for x in alfa:
    if not(x in s):
        neko = x
        break
print(neko)

Submission status: Accepted

Solution code:
S = list(input())
All = list("abcdefghijklmnopqrstuvwxyz")
res = list(set(S) ^ set(All))
if len(res) > 0:
    print(res[0])
else:
    print("None")

Submission status: Accepted

Solution code:
S = input().strip()

alpha = [chr(i) for i in range(ord("a"), ord("z")+1)]
d = {}
for i in alpha:
    d[i] = 0

for i in S:
    d[i] += 1

is_none = True
for i in alpha:
    if d[i] == 0:
        is_none = False
        print(i)
        break

if is_none:
    print("None")

Submission status: Accepted

Solution code:
S = set(input())

li = list({chr(ord('a') + i) for i in range(26)} - S)
li = sorted(li)

print(None) if len(li)==0 else print(li[0])

Submission status: Accepted

Solution code:
s = input()

n = len(s)
l = list()

for a in range(0, n):
    l.append(s[a])

l.sort()
l = list(set(l))
n = len(l)

if n == 26:
    print('None')
else:
    for a in range(0, n):
        l[a] = int(ord(l[a]))
    for a in range(97, 123):
        if a not in l:
            print(chr(a))
            break

Submission status: Accepted

Solution code:
import sys

S = input()
alphabet = list(map(chr, range(97, 97+26)))

for char in alphabet:
    if not char in S:
        print(char)
        sys.exit()

print('None')

Submission status: Accepted

Solution code:
alp=["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()
l=len(s)

for i in range(l):
    if s[i] in alp:
        alp.remove(s[i])

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

Submission status: Accepted

Solution code:
import sys
import string

input = sys.stdin.readline

def main():
    ans = 'None'
    S = input()
    s = string.ascii_lowercase
    for i in s:
        if i not in S:
            ans = i
            break
    print(ans)

if __name__ == '__main__':
    main()

Submission status: Accepted

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

for l in lists:
    if l not in S:
        print(l)
        exit()
print('None')

Submission status: Accepted

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

for l in lists:
    if S.find(l) == -1:
        print(l)
        exit()
print('None')

Submission status: Accepted

Solution code:
S = set(input())

for i in range(97,97+26):
    if chr(i) not in S:
        print(chr(i))
        exit()

print("None")

Submission status: Accepted

Solution code:
s = input()

t = "abcdefghijklmnopqrstuvwxyz"
s = sorted(set(s))
for tt in t:
    if tt not in s:
        print(tt)
        exit()
print('None')

Submission status: Accepted

Solution code:
s = input()
L = 'abcdefghijklmnopqrstuwxyz'
for i in s:
    L = L.replace(i, '')
if len(L) == 0:
    print('None')
else:
    print(L[0])

Submission status: Accepted

Solution code:
eng = 'abcdefghijklmnopqrstuvwxyz'
s = input()
for i in range(len(s)):
  eng = eng.replace(s[i], '')
  
if eng == '':
  print('None')
else:
  print(sorted(eng)[0])

Submission status: Accepted

Solution code:
S = input()

for i in range(ord("a"), ord("z") + 1):
  s = chr(i)
  if S.count(s) == 0:
    print(s)
    exit()
print("None")

Submission status: Accepted

Solution code:
s = input()
a = [True for _ in range(26)]
for si in s:
  a[ord(si)-97] = False
for i in range(26):
  if a[i]:
    print(chr(i+97))
    exit()
print('None')

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"]
A=list(input())
A=set(A)
for i in range(26):
    if l[i] in A:
        pass
    else:
        print(l[i])
        exit()
print("None")

Submission status: Accepted

Solution code:
s = input()
ans = 'None'
for letter in "abcdefghijklmnopqrstuvwxyz":
  if letter not in s:
    ans = letter
    break
print(ans)

Submission status: Accepted

Solution code:
#print#!/usr/bin/env python3
#%% for atcoder uniittest use
import sys
input= lambda: sys.stdin.readline().rstrip()
sys.setrecursionlimit(10**9)
def pin(type=int):return map(type,input().split())
def tupin(t=int):return tuple(pin(t))
def lispin(t=int):return list(pin(t))
#%%code

def resolve():
    S=input()
    a=ord("a")

    for i in range(26):
        temp=a+i
        for s in S:
            if s==chr(temp):break
        else:print(chr(temp));return
    print("None")
                

            
        
#%%submit!    
resolve()

Submission status: Accepted

Solution code:
def resolve():
    import string
    s = str(input())
    alpha = set(string.ascii_lowercase)
    for a in s:
        alpha.difference_update(a)

    try:
        print(sorted(alpha)[0])
    except IndexError:
        print('None')


resolve()

Submission status: Accepted

Solution code:
def main():
    s = list(input())
    li = list(chr(i)for i in range(97, 123))
    for i in li:
        if i not in s:
            print(i)
            exit()
    print('None')


if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
S1 = set(list('abcdefghijklmnopqrstuvwxyz'))
S2 = set(list(input()))
S3 = S1-S2
if len(S3) == 0:
    print('None')
else:
    print(sorted(list(S3))[0])

Submission status: Accepted

Solution code:
s=list(input())
l=list(chr(i)for i in range(97,123))
for i in l:
    if i not in s:
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
S = str(input())

chr = 'abcdefghijklmnopqrstuvwxyz'

res =""

for i in range(len(chr)):
    
    if chr[i] not in S:
        res = chr[i]
        break
    
if res =="":
    print("None")
else:
    print(res)

Submission status: Accepted

Solution code:
S=input()
alf=['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 alf:
    alf.remove(str(S[i]))
  
if len(alf)>0:
  print(alf[0])
  exit()
print('None')

Submission status: Accepted

Solution code:
import string

S = input()
l = []
char = string.ascii_lowercase

for c in char:
    if not c in S:
        l.append(c)

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

Submission status: Accepted

Solution code:
s = input()
a = 'abcdefghijklmnopqrstuvwxyz'
hoge_list = list(a)
s_list = list(s)
c = 0
s_s_list = set(s_list)
for hoge in hoge_list:
  if not hoge in s_s_list:
    c += 1
    print(hoge)
    break
if c == 0:
  print('None')

Submission status: Accepted

Solution code:
import sys
from string import ascii_lowercase as AL

input = sys.stdin.readline


def main():
    S = input().rstrip()

    counter = {}
    for s in AL:
        counter[s] = 0

    for s in S:
        counter[s] += 1

    ans = ""
    for s in AL:
        if counter[s] == 0:
            ans = s
            break
    if not ans:
        ans = "None"

    print(ans)


if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
s = list(input())

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

for i in range(len(alpha)):
    if not alpha[i]:
        print(chr(97 + i))
        break
    if i == 25:
        print("None")

Submission status: Accepted

Solution code:
S = list(input())

flg = True

for i in range(ord('a'), ord('z') + 1):
    if S.count(chr(i)) == 0:
        flg = False
        ans = chr(i)
        break

print("None" if flg else ans)

Submission status: Accepted

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

for char in alphabets:
  if char not in s:
    print(char)
    break
else:
  print('None')

Submission status: Accepted

Solution code:
# region header
import sys
import math
from bisect import bisect_left, bisect_right, insort_left, insort_right
from collections import defaultdict, deque, Counter
from copy import deepcopy
from fractions import gcd
from functools import lru_cache, reduce
from heapq import heappop, heappush
from itertools import accumulate, groupby, product, permutations, combinations, combinations_with_replacement
from math import ceil, floor, factorial, log, sqrt, sin, cos
from operator import itemgetter
from string import ascii_lowercase, ascii_uppercase, digits
sys.setrecursionlimit(10**7)
rs = lambda: sys.stdin.readline().rstrip()
ri = lambda: int(rs())
rf = lambda: float(rs())
rs_ = lambda: [_ for _ in rs().split()]
ri_ = lambda: [int(_) for _ in rs().split()]
rf_ = lambda: [float(_) for _ in rs().split()]
INF = float('inf')
MOD = 10 ** 9 + 7
PI = math.pi
# endregion
S = list(rs())
for i in ascii_lowercase:
    if not i in S:
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
a = [chr(ord("a") + i) for i in range(26)]
s = sorted(set(input()))

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

print("None")

Submission status: Accepted

Solution code:
import sys
S = sorted(set(input()))

alp = ['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(alp)):
  if (i>len(S)-1):
    print(alp[i])
    sys.exit()
  elif S[i] != alp[i]:
    print(alp[i])
    sys.exit()

print('None')

Submission status: Accepted

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

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

print("None")

Submission status: Accepted

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

Submission status: Accepted

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

if "".join(s) == a:
    print("None")
    exit()
else:
    for i in s:
        a = a.replace(i, "")

print(a[0])

Submission status: Accepted

Solution code:
a=[chr(ord('a') + i) for i in range(26)]
s=input()
ans=[]
for k in a:
    if k not in s:
        ans.append(k)
if not ans:
    print("None")
else:
    print(min(ans))

Submission status: Accepted

Solution code:
S = input()

s = set([c for c in S])

x = 'abcdefghijklmnopqrstuvwxyz'

for a in s:
    x = x.replace(a, '')
if len(x) == 0:
    print('None')
else:
    print(x[0])

Submission status: Accepted

Solution code:
s=input()
a="abcdefghijklmnopqrstuvwxyz"
for i in range(26):
  if a[i] in s:
    continue
  else:
    print(a[i])
    exit()
print("None")

Submission status: Accepted

Solution code:
S = sorted(list(set(list(input()))))
alpha = [int(i) for i in range(0,27)]
if len(S) == 26:
    print("None")
else:
    for i in range(0, 27):
        if chr(alpha[i]+97) not in S:
            print(chr(alpha[i]+97))
            break

Submission status: Accepted

Solution code:
import sys
import heapq, math
from itertools import zip_longest, permutations, combinations, combinations_with_replacement
from itertools import accumulate, dropwhile, takewhile, groupby
from functools import lru_cache
from copy import deepcopy

S = input()
use = [False] * 26

for s in S:
    use[ord(s) - 97] = True

def ans():
    for i in range(26):
        if not use[i]:
            return chr(i + 97)

    return "None"

print(ans())