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

Submission status: Accepted

Solution code:
import sys
import copy
import math
import itertools
import numpy as np
S = input()
for i in "abcdefghijklmnopqrstuvwxyz":
    if S.count(i) == 0:
        print(i)
        sys.exit(0)

print("None")

Submission status: Accepted

Solution code:
s = input()
d_l = [chr(i) for i in range(97, 97+26)]
ans = None
for d in d_l:
    if d not in list(s):
        ans = d
        break
print(ans)

Submission status: Accepted

Solution code:
s = str(input())
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 s:
  if i in L:
    L.remove(i)
if L == []:
  print('None')
else:
  print(L[0])

Submission status: Accepted

Solution code:
s = input()
cnt = 0
for i in range(26):
    if chr(97 + i) in s:
        cnt += 1
        if cnt == 26:
            print("None")
            break
    else:
        print(chr(97+i))
        break

Submission status: Accepted

Solution code:
L = [chr(i) for i in range(97, 123)]
f = 0
s = input()
for l in L:
  if s.count(l) == 0:
    print(l)
    f = 1
    break
if f == 0:
  print("None")

Submission status: Accepted

Solution code:
S = str(input())

no_ans = "None"
ans_list = []
arufabet = ["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(arufabet)):
    if arufabet[i] not in S:
        ans_list.append(arufabet[i])

if len(ans_list) == 0:
    print(no_ans)
else:
    print(ans_list[0])

Submission status: Accepted

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

ans = "None"
for i in range(97, 123):
    cnt = chr(i)
    if not cnt in S:
        ans = cnt
        break
        
print(ans)

Submission status: Accepted

Solution code:
def main():
    s = input()
    l = "abcdefghijiklmopqrstuvwxyz"

    for i in range(len(s)):
        l = l.replace(s[i], '')

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


if __name__ == "__main__":
    main()

Submission status: Accepted

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

Submission status: Accepted

Solution code:
S = input()

import string
lst = list(string.ascii_lowercase)
d = {lst[i]:i for i in range(len(lst))}
cnt = [0]*len(lst)

for ch in S:
  cnt[d[ch]] = 1
  
idx = -1
for i in range(len(cnt)):
  if cnt[i] == 0:
    idx = i
    break

if idx == -1:
  print("None")
else:
  print(lst[idx])

Submission status: Accepted

Solution code:
alphabet = [chr(i) for i in range(97, 123)]
S = set(list(input()))
for s in S:
  if s in alphabet: alphabet.remove(s)
    
print(alphabet[0]) if alphabet else print("None")

Submission status: Accepted

Solution code:
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)

import string

s = set(input().strip())
alpha = set(string.ascii_lowercase)
s = sorted(list(alpha - s))
if s:
    print(s[0])
else:
    print('None')

Submission status: Accepted

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

alphabet = list('abcdefghijklmnopqrstuvwxyz')

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

print('None')

Submission status: Accepted

Solution code:
s = sorted(set(input()))
a = len(set(s))
s.append(0)
for i in range(26):
    if s[i] != chr(97+i):
        print(chr(97+i))
        break
else:
    print('None')

Submission status: Accepted

Solution code:
S=input()
X=set([s for s in 'abcdefghijklmnopqrstuvwxyz'])
for s in S:
  X.discard(s)
X=list(X)
X.sort()
X.append('None')
print(X[0])

Submission status: Accepted

Solution code:
import sys
alphabet = "abcdefghijklmnopqrstuvwxyz"
s = set(sorted(input().strip()))
for i in alphabet:
    if not i in s:
        print(i)
        sys.exit()
print("None")

Submission status: Accepted

Solution code:
alp = "abcdefghijklmnopqrstuvwxyz"
ans = [False for _ in range(26)]
S = list(input())
for i in S:
    for p in range(26):
        if i == alp[p]:
            ans[p] = True
for i in range(26):
    if ans[i] == False:
        print(alp[i])
        break
else:
    print("None")

Submission status: Accepted

Solution code:
import math
from math import gcd,pi,sqrt
INF = float("inf")

import sys
sys.setrecursionlimit(10**6)
import itertools
from collections import Counter,deque
def i_input(): return int(input())
def i_map(): return map(int, input().split())
def i_list(): return list(i_map())
def i_row(N): return [i_input() for _ in range(N)]
def i_row_list(N): return [i_list() for _ in range(N)]
def s_input(): return input()
def s_map(): return input().split()
def s_list(): return list(s_map())
def s_row(N): return [s_input for _ in range(N)]
def s_row_str(N): return [s_list() for _ in range(N)]
def s_row_list(N): return [list(s_input()) for _ in range(N)]

import string

def main():
    a  = string.ascii_lowercase
    s = s_input()
    for i in a:
        if i not in s:
            print(i)
            exit()
    print("None")


if __name__=="__main__":
    main()

Submission status: Accepted

Solution code:
S = input()
a = "abcdefghijklmnopqrstuvwxyz"
ans = "None"
for x in a:
  if x not in S:
    ans = x
    break
print(ans)

Submission status: Accepted

Solution code:
# B - Not Found
S = input()
c = [0]*27
for i in range(len(S)):
    c[ord(S[i])-ord('a')] = 1
i = 0
while c[i]:
    i += 1
ans = chr(ord('a')+i) if i<26 else 'None'
print(ans)

Submission status: Accepted

Solution code:
#from statistics import median
#import collections
#aa = collections.Counter(a) # list to list || .most_common(2)で最大の2個とりだせるお a[0][0]
from fractions import gcd
from itertools import combinations,permutations,accumulate, product # (string,3) 3回
#from collections import deque
from collections import deque,defaultdict,Counter
import decimal
import re
import math
import bisect
#
#
#
# pythonで無理なときは、pypyでやると正解するかも！！
#
#
# my_round_int = lambda x:np.round((x*2 + 1)//2)
# 四捨五入g
#
# インデックス系
# int min_y = max(0, i - 2), max_y = min(h - 1, i + 2);
# int min_x = max(0, j - 2), max_x = min(w - 1, j + 2);
#
#
import sys
sys.setrecursionlimit(10000000)
mod = 10**9 + 7
#mod = 9982443453
#mod = 998244353
from sys import stdin
readline = stdin.readline
def readInts():
  return list(map(int,readline().split()))
def readTuples():
    return tuple(map(int,readline().split()))
def I():
  return int(readline())
ans = "abcdefghijklmnopqrstuvwxyz"
s = input()
s = sorted(list(set(s)))
for v in ans:
    flag = True
    for j in range(len(s)):
        if s[j] == v:
            flag = False
    if flag:
        print(v)
        exit()
print(None)

Submission status: Accepted

Solution code:
S = list(input())
L = len(S)
Slist = set()
for i in range(L):
    Slist.add(ord(S[i]))
Slist = list(Slist)
Slist.sort()
ans = "None"
j = 0
L = len(Slist)
for i in range(97, 123):
    if Slist[j] == i:
        j += 1
        if j >= L and i+1 < 123:
            ans = chr(i+1)
            break
        continue
    ans = chr(i)
    break
print(ans)

Submission status: Accepted

Solution code:
S = input()

a = [True for _ in range(26)]

for s in S:
    a[ord(s) - ord("a")] = False

for i, aa in enumerate(a):
    if aa:
        print(chr(i + ord("a")))
        exit()

print("None")

Submission status: Accepted

Solution code:
from collections import Counter

S = list(input())
ac = Counter(S)

alp = 'abcdefghijklmnopqrstuvwxyz'

for a in alp:
    if not(a in ac):
        print(a)
        break
else:
    print('None')

Submission status: Accepted

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

Submission status: Accepted

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

ans = ""
for i in range(len(l)):
  if ord(l[i]) !=  97 + i:
    ans = chr(97+i)
    break
  elif i == 25 and l[i] == "z":
    ans = "None"

if ans != "":
 print(ans)
else:
  print(chr(ord(l[-1])+1))

Submission status: Accepted

Solution code:
S = input().strip()
C = {chr(i):0 for i in range(97,123)}
for i in range(len(S)):
    C[S[i]] += 1
x = "None"
for i in range(97,123):
    if C[chr(i)]==0:
        x = chr(i)
        break
print(x)

Submission status: Accepted

Solution code:
from string import ascii_lowercase
S = 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(97,123):
	if not chr(i) in s:
		print(chr(i))
		exit()

print("None")

Submission status: Accepted

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

Submission status: Accepted

Solution code:
import sys
import math
import itertools
import collections
import heapq
import re
import numpy as np
from functools import reduce

rr = lambda: sys.stdin.readline().rstrip()
rs = lambda: sys.stdin.readline().split()
ri = lambda: int(sys.stdin.readline())
rm = lambda: map(int, sys.stdin.readline().split())
rl = lambda: list(map(int, sys.stdin.readline().split()))
inf = float('inf')
mod = 10**9 + 7

s = rr()
for char in 'abcdefghijklmnopqrstuvwxyz':
    if char not in s:
        print(char)
        exit()
else:
    print('None')

Submission status: Accepted

Solution code:
S=input()

alph="abcdefghijklmnopqrstuvwxyz"

for i in alph:
    if i in S:
        alph=alph.replace(i,"")

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

Submission status: Accepted

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

for i in alphabet:
    if i in s:
        alphabet = alphabet.replace(i,"")

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

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)) 
    exit()
print("None")

Submission status: Accepted

Solution code:
s = str(input())

alp = set("abcdefghijklmnopqrstuvwxyz")
s = set(s)
#print(s & alp)

if len(s & alp)==26:
    ans = "None"
else:
    lis = list(alp-s)
    lis.sort()
    ans = lis[0]

print(ans)

Submission status: Accepted

Solution code:
import sys

readline = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = float('INF')
sys.setrecursionlimit(10 ** 5)


def main():
    from string import ascii_lowercase

    s = set(input())
    t = set(ascii_lowercase)
    u = t - s

    if u:
        v = sorted(list(u))
        print(v[0])
    else:
        print("None")


if __name__ == '__main__':
    main()

Submission status: Accepted

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

S = sorted(set(list(input())))

ans = 'None'
for keyword in list("abcdefghijklmnopqrstuvwxyz"):
    hit = False
    for s in S:
        if s == keyword:
            hit = True
            break 
    
    if hit == False:
        ans = keyword
        break

print(ans)

Submission status: Accepted

Solution code:
A = [0 for i in range(26)]
S = input()
for s in S:
  A[ord(s)-97] = 1
flag = False
for i in range(26):
  if A[i]==0:
    flag = True
    break
if flag:
  print(chr(97+i))
else:
  print("None")

Submission status: Accepted

Solution code:
s=input()

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

Submission status: Accepted

Solution code:
S = list(input())

S.sort()

if S[0] != 'a':
    print('a')
elif S[0] == 'a':
    for i in range(len(S)-1):
        if ord(S[i+1]) - ord(S[i]) == 0 or ord(S[i+1]) - ord(S[i]) == 1:
            pass
        else:
            res = ord(S[i]) + 1
            print(chr(res))
            exit()
            
    res = ord(S[-1]) + 1

    if S[0] == 'a' and S[-1] == 'z':
        print('None')
    elif S[0] != 'a':
        print('a')
    else:
        print(chr(res))

Submission status: Accepted

Solution code:
import string

all_string = set(string.ascii_lowercase)
S = set(input())

ans = sorted(list(all_string - S))

print(ans[0]) if ans != [] else 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"]
l = list(set(alpha) - set(s))
l.sort()
print(l[0] if len(l) != 0 else "None")

Submission status: Accepted

Solution code:
S = input()

a = list('abcdefghijklmnopqrstuvwxyz')

n=[]
for i in a:
  if i not in S:
    n.append(i)
    
if len(n)==0:
  print('None')
  
else:
  print(min(n))

Submission status: Accepted

Solution code:
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']
s=str(input())
for i in range(len(a)):
  if a[i]not in s:
    print(a[i])
    exit()
print("None")

Submission status: Accepted

Solution code:
# vim: fileencoding=utf-8


def main():
    s = input()
    li = [0] * 26
    for i in list(s):
        n = ord(i) - ord("a")
        li[n] = 1
    for i in range(26):
        if li[i] == 0:
            print(chr(i + ord("a")))
            return

    print("None")


if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
s= input()

for i in range(ord('a'), ord('z') + 1):
    if s.count(chr(i)) == 0:
        print(chr(i))
        exit()

print('None')

Submission status: Accepted

Solution code:
S = input()

ans = "None"

for i in range(ord("a"), ord("z") + 1):
    if not chr(i) in S:
        ans = chr(i)
        break
print(ans)

Submission status: Accepted

Solution code:
S = input()

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

Submission status: Accepted

Solution code:
S = input()
alp = 'abcdefghijklmnopqrstuvwxyz'
rst = 'None'
for i in alp:
	if not i in S:
		rst = i
		break
print(rst)

Submission status: Accepted

Solution code:
import string

S = list(input())

low_list = list(string.ascii_lowercase)
for i in range(len(S)):
    try:
        low_list.remove(S[i])
    except ValueError:
        pass

if len(low_list) == 0:
    print('None')
else:
    print(low_list[0])

Submission status: Accepted

Solution code:
s=input()
al=['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 al[i] not in s:
    print(al[i])
    exit()
print('None')

Submission status: Accepted

Solution code:
s = input()

a = ord('a')

t = set()
for c in s:
    t.add(ord(c) - a)

for i in range(26):
    if not i in t:
        print(chr(a + i))
        exit()

print("None")

Submission status: Accepted

Solution code:
s=input()
alpha="abcdefghijklmnopqrstuvwxyz"
res="None"
for i in alpha:
    if not i in s:
        res=i
        break
print(res)

Submission status: Accepted

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

s.sort()

for i in range(26):
    if i >= len(s) or s[i] != chr(i + ord('a')):
        print(chr(i + ord('a')))
        exit()
else:
    print('None')

Submission status: Accepted

Solution code:
n = input()
a = list('abcdefghijklmnopqrstuvwxyz')
a = set(a)
v = []
for i in a:
    if not i in n:
        v.append(i)
if len(v) == 0:
    print('None')
else:
    v.sort()
    print(v[0])

Submission status: Accepted

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


def main():
    a = set("abcdefghijklmnopqrstuvwxyz") - set(input())
    if a == set():
        print("None")
        exit(0)
    print(sorted(list(a))[0])


main()

Submission status: Accepted

Solution code:
s=str(input())
X="abcdefghijklmnopqrstuvwxyz"
Y=[]
for i in range(len(X)):
    Y.append(X[i])
for i in range(len(X)):
    if X[i] in s:
        Y.remove(X[i])


if len(Y)==0:
    print("None")

else:
    print(Y[0])

Submission status: Accepted

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

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

Submission status: Accepted

Solution code:
def main():
    s = input()
    s = sorted(s)
    ascii_lowercase = 'abcdefghijklmnopqrstuvwxyz'
    ans = 'None'
    for chr_alpha in ascii_lowercase:
        if chr_alpha not in s:
            ans = chr_alpha
            break
    print(ans)


if __name__ == "__main__":
    main()

Submission status: Accepted

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

Submission status: Accepted

Solution code:
S = input()

s_list = [s for s in S]
c_list = [c for c in "abcdefghijklmnopqrstuwvxyz"]

answer = "None"
for c in c_list:
  if c not in s_list:
    answer = c
    break

print(answer)

Submission status: Accepted

Solution code:
s = input()
alpha = "abcdefghijklmnopqrstuvwxyz"
for a in alpha:
    if a not in s:
        print(a)
        break
else:
    print("None")

Submission status: Accepted

Solution code:
import string
S = list(input())
ar = string.ascii_lowercase
for w in ar:
  if w not in S:
    print(w)
    exit()
print('None')

Submission status: Accepted

Solution code:
s = list(input())
s.sort()
a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'r', '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()
print('None')

Submission status: Accepted

Solution code:
s=input()

alp="abcdefghijklmnopqrstuvwxyz"

ans="None"
for i in alp:
  if i not in s:
    ans=i
    break
    
print(ans)

Submission status: Accepted

Solution code:
s = list(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()

alphabet="abcdefghijklmnopqrstuvwxyz"

ans = "None"

for i in range(len(alphabet)):
    if alphabet[i] in S:
        continue
    else:
        ans = alphabet[i]
        break
print(ans)

Submission status: Accepted

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

for c in str:
    found = False
    for s in S:
       if s == c:
           found = True
           break
    if found:
        continue
    else:
        print(c)
        exit()

print('None')

Submission status: Accepted

Solution code:
s = str(input())
ans = 'None'
for j in range(97, 123):
    if chr(j) in s:
        continue
    else:
        ans = chr(j)
        break
print(ans)

Submission status: Accepted

Solution code:
S = input()
S = sorted(S)
ans = 'None'
for i in range(97, 123):
    if S.count(chr(i)) > 0:
      continue
    else:
      ans = chr(i)
      break
print(ans)

Submission status: Accepted

Solution code:
s=input()
l='abcdefghijklmnopqrstuvwxyz'
for i in range(26):
    if(s.count(l[i])==0):
        print(l[i])
        exit()
print('None')

Submission status: Accepted

Solution code:
s=input()
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(len(s)):
  try:
    l.remove(s[i])
  except:
    continue
try:
  print(l[0])
except:
  print("None")

Submission status: Accepted

Solution code:
S = input()
N = len(S)

X = set()
ans = 'None'

for i in range(N):
    X.add(S[i])

for alph in ['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 alph not in X:
             ans = alph
             break

print(ans)

Submission status: Accepted

Solution code:
s = input()

for i in range(26):
    x = chr(i + 97)
    if not x in s:
        print(x)
        exit()
print('None')

Submission status: Accepted

Solution code:
S=list(input())
data=['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(data)):
    if data[i] not in S:
        print(data[i])
        break
else:
    print('None')

Submission status: Accepted

Solution code:
a=list(input())
n=[]
for i in range(97, 123):
    n.append(chr(i))
a=list(set(a))
ans=[]
for i in n:
    if i not in a:
        ans.append(i)
if ans==[]:
    print('None')
else:
    print(ans[0])

Submission status: Accepted

Solution code:
S = input()
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 x in l:
    if x not in S:
        print(x)
        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']
l = []
for i in alpha:
    if i not in s:
        l.append(i)

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

Submission status: Accepted

Solution code:
S = input()
l = 'abcdefghijklmnopqrstuvwxyz'
for i in range(len(l)):
    if l[i] not in S:
        print(l[i])
        exit(0)
else:
    print('None')

Submission status: Accepted

Solution code:
import sys,collections as cl,bisect as bs
sys.setrecursionlimit(100000)
input = sys.stdin.readline
mod = 10**9+7
Max = sys.maxsize
def l(): #intのlist
    return list(map(int,input().split()))
def m(): #複数文字
    return map(int,input().split())
def onem(): #Nとかの取得
    return int(input())
def s(x): #圧縮
    a = []
    if len(x) == 0:
        return []
    aa = x[0]
    su = 1
    for i in range(len(x)-1):
        if aa != x[i+1]:
            a.append([aa,su])
            aa = x[i+1]
            su = 1
        else:
            su += 1
    a.append([aa,su])
    return a
def jo(x): #listをスペースごとに分ける
    return " ".join(map(str,x))
def max2(x): #他のときもどうように作成可能
    return max(map(max,x))
def In(x,a): #aがリスト(sorted)
    k = bs.bisect_left(a,x)
    if k != len(a) and a[k] ==  x:
        return True
    else:
        return False

def pow_k(x, n):
    ans = 1
    while n:
        if n % 2:
            ans *= x
        x *= x
        n >>= 1
    return ans

"""
def nibu(x,n,r):
    ll = 0
    rr = r
    while True:
        mid = (ll+rr)//2

    if rr == mid:
        return ll
    if (ここに評価入れる):
        rr = mid
    else:
        ll = mid+1
"""

ss = list(input()[:-1])

ss.sort()

aaa = s(ss)

ima = set()

for i in aaa:
    ima.add(i[0])

data = "qwertyuiopasdfghjklzxcvbnm"

se = set()
for i in data:
    se.add(i)
ans = se - ima

ans = sorted(list(ans))

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

Submission status: Accepted

Solution code:
import string

s = set(sorted(input()))

for i in string.ascii_lowercase:
    if i not in s:
        print(i)
        exit()
print("None")

Submission status: Accepted

Solution code:
a = "abcdefghijklmnopqrstuvwxyz"
S = str(input())
l = []

for i in range(26):
    if not a[i] in S:
        l.append(i)

if not l:
    print('None')

else:
    print(a[min(l)])

Submission status: Accepted

Solution code:
S=list(str(input()))
x="abcdefghijklmnopqrstuvwxyz"
ans="None"
for i in range(len(x)):
    if x[i] not in S:
        ans=x[i]
        break
print(ans)

Submission status: Accepted

Solution code:
import numpy as np
S=input()

num=np.zeros(26)
for i in range(len(S)):
    num[int(ord(S[i]))-97]+=1

zero=[i for i, num in enumerate(num) if num==0]
if zero==[]:
    print("None")
else:
    print(chr(zero[0]+97))

Submission status: Accepted

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

x = 0
for c in 'abcdefghijklmnopqrstuvwxyz':
  if c not in A:
    print(c)
    x = 1
    break
if x == 0:
  print('None')

Submission status: Accepted

Solution code:
s=input();n=[chr(i) for i in range(97,123) if chr(i) not in s];print(n[0] if n else '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 alpha :
    if (i in S) == False :
        print(i)
        exit()
print('None')

Submission status: Accepted

Solution code:
s = input ()
x = 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 (len(l)):
  if s.count(l[i]) == 0:
    print (l[i])
    x = 1
    break
if x == 0:
  print ('None')

Submission status: Accepted

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

Submission status: Accepted

Solution code:
S = input()
exist = [False] * 26
char = "abcdefghijklmnopqrstuvwxyz"
for i in range(len(S)):
    for j in range(26):
        if S[i] == char[j]:
            exist[j] = True
            break
for i in range(26):
    if exist[i] == False:
        print(char[i])
        exit()
print("None")

Submission status: Accepted

Solution code:
import collections

S = list(input())

c = collections.Counter(S)

ans = " "
for i in range(97,123):
    s = chr(i)

    if s in c:
        continue
    else:
        ans = s
        break

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

Submission status: Accepted

Solution code:
import sys
s=list(input())
t=set(s)

r='abcdefghijklmnopqrstuvwxyz'

for i in range(26):
  if r[i] not in t:
    print(r[i])
    sys.exit()
    
print('None')

Submission status: Accepted

Solution code:
s = input()

import string
a = list(string.ascii_lowercase)

for item in a:
    if item not in s:
        print(item)
        break
else:
    print('None')

Submission status: Accepted

Solution code:
S = list(input())
Sd = {i:S[i] for i in range(len(S))}
check = {i:0 for i in range(26)}
ans = -1

for k,v in Sd.items():
    check[ord(v)-ord('a')] = 1
    
for k,v in check.items():
    if v == 0:
        ans = k
        break
        
if ans == -1:
    print('None')
else:
    print(chr(ans+ord('a')))

Submission status: Accepted

Solution code:
S = input()

for i in range(97, 123):
    if chr(i) not in S:
        print(chr(i))
        exit()
print('None')

Submission status: Accepted

Solution code:
def resolve():
    '''
    code here
    '''
    import string
    abc = string.ascii_lowercase

    S = input()

    
    for item in abc:
        if item not in S:
            print(item)
            break
    else:
        print('None')




if __name__ == "__main__":
    resolve()

Submission status: Accepted

Solution code:
from collections import defaultdict,deque
import math
def main():
    alph = "abcdefghijklmnopqrstuvwxyz"
    s = input()

    for i in range(26):
        if(s.count(alph[i])==0):
            print(alph[i])
            exit()
    print("None")

if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
alpha_dict = {}
for i,c in enumerate(range(ord('A'),ord('Z')+1)):
  alpha_dict[chr(c).lower()] = 0

s = list(input())
for i in range(len(s)):
  alpha_dict[s[i]] += 1

for k, v in alpha_dict.items():
  if v == 0:
    print(k)
    exit()
print('None')

Submission status: Accepted

Solution code:
alphabeta = "abcdefghijklmnopqrstuvwxyz"
all_str  = set(alphabeta) 
str = input() 
str = set(str)


use = all_str-str 
if use == set():
  print("None")
else:
  print(sorted(use)[0])

Submission status: Accepted

Solution code:
L=list(input())
L=list(set(L))
L=sorted(L)
R=["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(min(26,len(L))):
  if L[i]!=R[i]:
    print(R[i])
    exit()
if len(L)<26:
  print(R[len(L)])
  exit()
print("None")

Submission status: Accepted

Solution code:
S = input()
alpha = []

for i in range(97,123):
    alpha.append(chr(i))
    
ans = []
for j in alpha:
    if not j in S:
        ans.append(j)
ans.append(None)

print(ans[0])

Submission status: Accepted

Solution code:
S = sorted(list(set(input())))
ABC = [chr(i) for i in range(97, 123)]
S_box = ["F" for i in range(26)]
ans = "None"
for i in range(26):
    for j in range(len(S)):
        if S[j] == ABC[i]:
            S_box[i] = ABC[i]
if len(S) == 26:
    pass
else:
    for i in range(26):
        if S_box[i] == "F":
            ans = ABC[i]
            break            
print(ans)

Submission status: Accepted

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

if len(set(S)) == 26:
    print("None")
    exit()

S = sorted(list(set(S)))

s = list("abcdefghijklmnopqrstuvwxyz")

def list_difference(list1, list2):
    result = list1.copy()
    for value in list2:
        if value in result:
            result.remove(value)

    return result

result = list_difference(s,S)

print(result[0])

Submission status: Accepted

Solution code:
s = input()
s = sorted(s)
ascii_lowercase = 'abcdefghijklmnopqrstuvwxyz'
ans = 'None'
for chr_alpha in ascii_lowercase:
  if chr_alpha not in s:
    ans = chr_alpha
    break
print(ans)

Submission status: Accepted

Solution code:
str1=input()

str2="abcdefghijklmnopqrstuvwxyz"


aaa=[]

for i in str2:
    #print(i)
    if (i in str1) == False:
        aaa.append(i)

aaa.sort()

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

Submission status: Accepted

Solution code:
S = input()
ans = ["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 len(set(S))==26:
    print("None")
else:
    ans = set(ans) ^ set(S)
    print(sorted(ans)[0])

Submission status: Accepted

Solution code:
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"]
b = input()
c = []
d = len(b)

for i in range(int(d)):
  c.append(b[i])

e = list(set(c))
f = sorted(e)
g = len(f)
h = int(0)

if g != 26:
  for i in range(int(g)):
    if f[i] == a[i]:
      h = h + 1
    else:
      print(a[i])
      break
else:
  print("None")
  
if h == g:
  print(a[h])

Submission status: Accepted

Solution code:
s = input()
t = sorted(set(list(s)))
if len(set(s)) >= 26:
    print("None")
    exit()

alp = [chr(i) for i in range(97, 97+26)]
for i in alp:
    if i not in t:
        print(i)
        exit()

Submission status: Accepted

Solution code:

def resolve():
    import sys
    import string
    input = sys.stdin.readline
    # row = [int(x) for x in input().rstrip().split(" ")]
    # n = int(input().rstrip())
    s = input().rstrip()
    alphabets = set()
    for c in string.ascii_lowercase:
        alphabets.add(c)

    for c in s:
        if c in alphabets:
            alphabets.remove(c)
            if len(alphabets) == 0:
                print("None")
                return

    print(sorted(alphabets)[0])

if __name__ == "__main__":
    resolve()

Submission status: Accepted

Solution code:
import string

s = list(input())
c = [chr(i) for i in range(97, 97+26)]
count = 0

for i in c:
    if i not in s:
        print(i)
        break
    else:
        count += 1

if count == 26:
    print("None")
else:
    pass

Submission status: Accepted

Solution code:
#n = int(input())
#a, b = map(int,input().split())
#l = list(map(int,input().split()))
#l = [list(map(int,input().split())) for i in range(n)]
s=list(input())
flag='None'
alphabet=list('abcdefghijklmnopqrstuvwxyz')
dic={}
for si in s:
    dic[si]=True

for c in alphabet:
    if dic.get(c,False)==False:
        flag=c
        break
print(flag)