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

Solution (Python):
alphabet = [chr(ord('a') + i) for i in range(26)]
s = list(input())
s = sorted(list(set(s)))
if len(s) == 26:
    print("None")
    exit()
for i in range(len(s)):
    if i == len(s) - 1:
        if s[i] == alphabet[i]:
            print(alphabet[i+1])
        else:
            print(alphabet[i])
        exit()
    if s[i] == alphabet[i]:
        pass
    else:
        print(alphabet[i])
        exit()

Solution (Python):
alphabet = [chr(ord('a') + i) for i in range(26)]
s = list(input())
s = sorted(list(set(s)))
if len(s) == 26:
    print("None")
    exit()
for i in range(len(s)):
    if s[i] == alphabet[i]:
        pass
    else:
        print(alphabet[i])
        exit()
print(alphabet[i+1])
exit()

Solution (Python):
s = input()

dicts = {i: False for i in range(ord('a'), ord('z') + 1)}

for i in s:
    if not dicts[ord(i)]:
        dicts[ord(i)] = True

for i in range(ord('a'), ord('z') + 1):
    if not dicts[i]:
        print(chr(i))
        exit()
print('None')

Solution (Python):
list_N = set(input())
lower_cha = set([chr(ord('a') + i) for i in range(26)])

ans = list(lower_cha-list_N)
ans.sort()
if len(ans) == 0:
    print("None")
else:
    print(ans[0])

Solution (Python):
d=set(input())
s="".join(sorted(list(d)))
for i in range(26):
    if chr(ord("a")+i) not in d:print(chr(ord("a")+i));break
else:print("None")

Solution (Python):
s=input()
al = list('abcdefghijklmnopqrstuvwxyz')
for s0 in s:
    if s0 in al:
        al.remove(s0)
if len(al) == 0:
    print(None)
else:
    print(al[0])

Solution (Python):
s = str(input())
S = [s[i] for i in range(len(s))]
S.sort()
S = set(S)
fr = 0
count = [chr(i) for i in range(97, 97+26)]
for i in count:
    if i in S:
        pass
    else:
        print(i)
        fr += 1
        break
if fr == 0:
    print('None')

Solution (Python):
import sys
import os

ii = lambda: int(sys.stdin.buffer.readline().rstrip())
il = lambda: list(map(int, sys.stdin.buffer.readline().split()))
fl = lambda: list(map(float, sys.stdin.buffer.readline().split()))
iln = lambda n: [int(sys.stdin.buffer.readline().rstrip()) for _ in range(n)]

iss = lambda: sys.stdin.buffer.readline().decode().rstrip()
sl = lambda: list(map(str, sys.stdin.buffer.readline().decode().split()))
isn = lambda n: [sys.stdin.buffer.readline().decode().rstrip() for _ in range(n)]

MOD = 10 ** 9 + 7


def main():
    if os.getenv("LOCAL"):
        sys.stdin = open("input.txt", "r")

    S = list(iss())
    for n in range(ord('a'), ord('z') + 1):
        if chr(n) not in S:
            print(chr(n))
            exit()
    else:
        print('None')


if __name__ == '__main__':
    main()

Solution (Python):
import string
t = list(string.ascii_lowercase)
s = input()

def find(s):
    for i in t:
        if s.count(i) == 0:
            return i
    return 'None'

print(find(s))

Solution (Python):
s=input()

sets=set(s)

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

Solution (Python):
s=input()
a=[chr(i) for i in range(ord("a"),ord("z")+1) if chr(i) not in s]
print("None" if len(a)==0 else a[0])

Solution (Python):
s=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"]

for i in range(len(s)):
  if s[i] in ls:
    ls.remove(s[i])
    
if len(ls)>0:
  print(ls[0])
  
else:
  print("None")

Solution (Python):
s=list(set(list(input())))
s.sort()
alphabet=list("abcdefghijklmnopqrstuvwxyz")
for i in s:
    alphabet.remove(i)
    
if alphabet==[]:
    print("None")
else:
    print(alphabet[0])

Solution (Python):
s=set(list(input()))
a=set([chr(i+97) for i in range(26)])
a-=s
print(sorted(list(a))[0] if len(a)!=0 else "None")

Solution (Python):
s=str(input())
ch=[]
for c in 'abcdefghijklmnopqrstuvwxyz':
    ch.append(c)

for c in s:
    if c in ch:
        del ch[ch.index(c)]

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

Solution (Python):
s = list(input())
if len(set(s)) == 26:
    print('None')
else:
    l = 'abcdefghijklmnopqrstuvwxyz'
    for i in l:
        if i in s:
            continue
        else:
            print(i)
            exit()

Solution (Python):
import string
print((sorted(set(string.ascii_lowercase)-set(input()))+[None])[0])

Solution (Python):
import string
print((sorted(set(string.ascii_lowercase) - set(input())) + ["None"])[0])

Solution (Python):
S = list(input())
ans = "None"
alphabets = ["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 item in alphabets:
    if not item in S:
        ans = item
        break

print(ans)

Solution (Python):
s = sorted(input())
t=[]
tf = [False]*(97+26+1)


for i in range(len(s)):
  t.append(ord(s[i]))
x=97
for i in set(t):
  tf[i]=True

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

Solution (Python):
s = input()

set_s = set(list(s))
x = 'abcdefghijklmnopqrstuvwxyz'

r = None
for i in x:
  if i not in sorted(list(s)) :
    r = i
    break
    
print(r)

Solution (Python):
import sys
s = input()
l = "abcdefghijklmnopqrstuvwxyz"
for i in range (len(l)):
    count = 0
    for j in range (len(s)):
        if(l[i] == s[j]):
            count += 1
            break
    if (count == 0):
        print(l[i])
        sys.exit()
print("None")

Solution (Python):
S=set(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"}
D=sorted(list(A-S))
if len(D)==0:
  print("None")
else:
  print(D[0])

Solution (Python):
s = input()

ans = []

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

print("None")

Solution (Python):
A = set(list(input()))
a = ord('a')
for i in range(26):
    c = chr(a + i)
    if c not in A:
        ans = c
        break
else:
    ans = 'None'
print(ans)

Solution (Python):
s = input()

ans = []

for i in range(ord("a"), ord("z")+1):
    if not chr(i) in s:
        ans.append(chr(i))

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

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

Solution (Python):
s = set(input())
alp = "abcdefghijklmnopqrstuvwxyz"
alpl = [i for i in alp]
for i in s:
    if i in alp:
        alpl.remove(i)
if len(alpl) != 0:        
    print(sorted(alpl)[0])

else:
    print("None")

Solution (Python):
import collections
s = input()
s = collections.Counter(s)
alphabet = "abcdefghijklmnopqrstuvwxyz"
for i in alphabet:
  if s[i] == 0:
    print(i)
    exit()
print("None")

Solution (Python):
s = str(input())
chars = set([c for c in s])

ans = 'None'
for i in range(ord('a'), ord('z')+1):
  
  if chr(i) not in chars:
    ans = chr(i)
    break
print(ans)

Solution (Python):




"""def kiri(n,m):
  r_ = n / m
  if (r_ - (n // m)) > 0:
    return (n//m) + 1
  else:
    return (n//m)"""








def main():
  
  
  
  s = input()
  dic = {}
  for a in s:
    if not a in dic.keys():
      dic[a] = 1
    else:
      pass
  for i in range(97,123):
    if not str(chr(i)) in dic.keys():
      print(chr(i))
      exit()
  print('None')
      
if __name__ == '__main__':
  main()

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

Solution (Python):
S = input()


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

Solution (Python):

import math
import itertools
import statistics

import collections



s = input()
alf = ["a","b", "c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","i","s","t","u","v","w","x","y","z"]
have = []
for i in range(len(s)):
    for j in range(len(alf)):
        if s[i]==alf[j]:
            have.append(alf[j])

have = list(set(have))
for i in range(len(alf)):
    if not(alf[i] in have):
        print(alf[i])
        exit()
print("None")

Solution (Python):
import string

s = set(input())

abc = set(string.ascii_lowercase)
rest = abc - s

if rest:
  print(min(rest))
else:
  print('None')

Solution (Python):
S = list(input())
S.sort()
l = list("abcdefghijklmnopqrstuvwxyz")
flag = 0

for i in l:
  if i in S:
    continue
  else:
    print(i)
    flag = 1
    break
    
if flag == 0:
  print("None")

Solution (Python):
s=list(input())
a=[chr(i) for i in range(97, 97+26) if chr(i) not in s]
if len(a)==0:print('None')
else:print(a[0])

Solution (Python):
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"]
s=list(input())
s.sort()
cnt=0
for i in alpha:
    if i not in s:
        print(i)
        cnt+=1
        break
    else:
        continue
if cnt==0:
    print("None")

Solution (Python):
alph = [chr(i) for i in range(97, 97+26)]

s = input()
s_li = set(sorted(list(s)))

for v in alph:
    if v not in s_li:
        print(v)
        exit(0)
print('None')

Solution (Python):
import string
s = set(input())
alp = sorted(string.ascii_lowercase,reverse=True)
ans = 'None'
for i in alp:
    if not i in s:
        ans = i
print(ans)

Solution (Python):
s=input()
l='abcdefghijklmnopqrstuvwxyz'
a=True
for i in range(26):
    if s.count(l[i])==0:
        print(l[i])
        a=False
        break
if a==True:
    print('None')

Solution (Python):
S = input()
s = set(S)
base = "abcdefghijklmnopqrstuvwxyz"
Base = set(list(base))
ans = set(Base.difference(s))
if len(s) == 26:
    ans = None
else:
    ans = min(ans)
print(ans)

Solution (Python):
s = input()
ans = "None"

for i in range(26):
    test = i + 97
    if chr(test) not in s:
        ans = chr(test)
        break

print(ans)

Solution (Python):
s=input()
a=sorted("qwertyuiopasdfghjklzxcvbnm")

b=sorted(list(set(s)))
for x in a:
    if not x in b:
        print(x)
        break
else:
    print("None")

Solution (Python):
s = input()
alp = [ 0 for _ in range(27) ]
for ss in s:
    alp[ord(ss)-ord("a")] += 1

for i in range(27):
    if i == 26:
        print("None")
        break
    if alp[i] == 0:
        print(chr(ord("a")+i))
        break

Solution (Python):
s = input()

flg = True
for i in "abcdefghijklmnopqrstuvwxyz":
    if i not in s:
        print(i)
        flg = False
        break

if flg:
    print("None")

Solution (Python):
s=set(input())
a=[]
for i in s:
  a.append(ord(i)-ord("a"))
for i in range(26):
  if i not in a:
    print(chr(i+ord("a")))
    break
if len(a)==26:
  print("None")

Solution (Python):
s = input()
alp = "abcdefghijklmnopqrstuvwxyz"
for i in alp:
	if i not in s:
		print (i)
		exit()
print ("None")

Solution (Python):
S=input()
alpha="abcdefghijklmnopqrstuvwxyz"
l=[]
for s in alpha:
    if s not in S:
        l.append(s)
if len(l)==0:
    print("None")
    exit()
l.sort()
print(l[0])

Solution (Python):












mod = int(1e9+7)
INF = 1<<29
lINF = 1<<35

def main():
    s = input()
    for i in range(ord('a'),ord('z')+1):
        res = 1
        for j in range(len(s)):
            if s[j]==chr(i):
                res = 0
                break
        if res:
            print(chr(i))
            return 0
    print("None")
    return

if __name__=='__main__':
    main()

Solution (Python):
from sys import exit
alphabet = "abcdefghijklmnopqrstuvwxyz"
S = input()
for i in alphabet:
  if i not in S:
    print(i)
    exit()
print("None")

Solution (Python):
S = list(set(list(input())))
S.sort(reverse=False)
n = 97

for i in range(len(S)):
  if S[i] != chr(n):
    print(chr(n))
    exit()
  n += 1

if len(S) == 26:
	print('None')
else:
	print(chr(n))

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

Solution (Python):
import sys

S = input()
alfa = [chr(i) for i in range(97, 97+26)]
l = [0] * 26

for i in range(len(S)):
    index = alfa.index(S[i])
    l[index] += 1

for i in range(len(l)):
    if l[i] == 0:
        print(alfa[i])
        sys.exit()
print("None")

Solution (Python):
a=set([chr(i) for i in range(97, 97+26)])
s=list(input())
for i in set(s):
    a.remove(i)
if a==set():
    print("None")
else:
    b=sorted(list(a))
    print(b[0])

Solution (Python):
s=input()
freq=[0]*26
for i in s:
    freq[ord(i)-ord('a')]=1
if sum(freq)==26:
    print('None')
else:
    for i in range(26):
        if freq[i]==0:
            print(chr(ord('a')+i))
            break

Solution (Python):
s = set(list(input()))
b = set(list("abcdefghijklmnopqrstuvwxyz"))

l = sorted(list(b-s))

if l == []:
  print("None")
else:
  print(sorted(list(b-s))[0])

Solution (Python):
s = input()

li = [0] * 26

for i in range(len(s)):
    s1 = s[i]
    li[ord(s1) - 97] += 1

for i in range(26):
    if li[i] == 0:
        print(chr(i+97))
        exit()

print('None')

Solution (Python):


import sys
 
stdin = sys.stdin
inf = 1 << 60
mod = 1000000007
 
ni      = lambda: int(ns())
nin     = lambda y: [ni() for _ in range(y)]
na      = lambda: list(map(int, stdin.readline().split()))
nan     = lambda y: [na() for _ in range(y)]
nf      = lambda: float(ns())
nfn     = lambda y: [nf() for _ in range(y)]
nfa     = lambda: list(map(float, stdin.readline().split()))
nfan    = lambda y: [nfa() for _ in range(y)]
ns      = lambda: stdin.readline().rstrip()
nsn     = lambda y: [ns() for _ in range(y)]
ncl     = lambda y: [list(ns()) for _ in range(y)]
nas     = lambda: stdin.readline().split()

from collections import Counter
import string

s = ns()
c = Counter(s)
d = dict(c)

ans = '$'
for i in range(len(string.ascii_lowercase)):
    if d.get(string.ascii_lowercase[i], 0) == 0:
        ans = string.ascii_lowercase[i]
        break
print("None" if ans == "$" else ans)

Solution (Python):
s=input()
li="abcdefghijklmnopqrstuvwxyz"

for i in range(len(li)):
    if li[i] not in s:
        print(li[i])
        exit()

print("None")

Solution (Python):
S = set(input())
alpha = set('abcdefghijklmnopqrstuvwxyz')
if S == alpha:
  print('None')
else:
  ans = sorted(alpha - S)
  print(ans[0])

Solution (Python):
S=input()
al=[chr(ord('a') + i) for i in range(26)]
ss=set(al)

for str in S:
  if str in ss:
    ss.remove(str)

if len(ss)>0:
  print(sorted(ss)[0])
else:
  print("None")

Solution (Python):
S=sorted(set(input()))
ans=None
for i in range(97,97+26):
  if chr(i) not in S:
    ans=chr(i)
    break
print(ans)

Solution (Python):
S=input()



for i in range(26):
    c = chr(ord('a') + i)
    if S.count(c) == 0:
        print(c)
        exit(0)
print('None')

Solution (Python):
a=set(range(26))-set([ord(i)-97for i in input()])
print(chr(min(a)+97)if a else'None')

Solution (Python):
a=set(range(26))-set([ord(i)-97for i in input()])
print('abcdefghijklmnopqrstuvwxyz'[min(a)]if a else'None')

Solution (Python):
s = input()
for k in range(26):
    c = chr(ord('a') + k)
    if s.count(c) == 0:
        print(c)
        exit(0)
print("None")

Solution (Python):
s=input()

s=list(s)
    
alf = [chr(ord('a') + i) for i in range(26)]

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

Solution (Python):
alp=set(list("abcdefghijklmnopqrstuvwxyz"))
S=alp - set(list(input()))
print("None" if len(S)==0 else min(S))

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

Solution (Python):
s=input()
l=[chr(i) for i in range(ord('a'),ord('z')+1) if chr(i) not in s]
print(l[0] if len(l) else 'None')

Solution (Python):
s = input()
a = list("abcdefghijklmnopqrstuvwxyz")
for i in sorted(s):
    if i in a:
        a.remove(i)

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

Solution (Python):
import collections

s = input()

col = collections.Counter(s)

for c in "abcdefghijklmnopqrstuvwxyz":
    if c not in col:
        print(c)
        exit()

print("None")

Solution (Python):
a = input()
a_l = 'abcdefghijklmnopqrstuvwxyz'
for i in range(26):
  if a.count(a_l[i])>=1:
    continue
  else:
    print(a_l[i])
    exit()
print('None')

Solution (Python):
def check(S):
  for i in range(97, 123):
    if chr(i) not in S:
      return chr(i)
  return 'None'


if __name__ == "__main__":
  S = set(input())
  print(check(S))

Solution (Python):
s = list(input())
a = [chr(ord('a') + i) for i in range(26)]
cnt = [0]*26
for i in range(len(s)):
    ind = a.index(s[i])
    cnt[ind] += 1
for i in range(len(cnt)):
    if cnt[i] == 0:
        print(a[i])
        exit()
print("None")

Solution (Python):

import sys


def solve(S: str):
    a = {chr(c) for c in range(ord("a"), ord("z") + 1)} - set(S)
    print(sorted(a)[0] if a else "None")


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = next(tokens)  
    solve(S)


if __name__ == '__main__':
    main()

Solution (Python):
s = set(input())
s = list(s)
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"]
l = len(s)
for i in range(l):
  list.remove(s[i])
if list ==[]:
  print('None')
else:
  print(list[0])

Solution (Python):
s = input().strip()
chars = list(set(s))
chars.sort()
dic = {"a": 0,
       "b": 1,
       "c": 2,
       "d": 3,
       "e": 4,
       "f": 5,
       "g": 6,
       "h": 7,
       "i": 8,
       "j": 9,
       "k": 10,
       "l": 11,
       "m": 12,
       "n": 13,
       "o": 14,
       "p": 15,
       "q": 16,
       "r": 17,
       "s": 18,
       "t": 19,
       "u": 20,
       "v": 21,
       "w": 22,
       "x": 23,
       "y": 24,
       "z": 25
       }
swap = {v: k for k, v in dic.items()}
ans = "None"
count = 0
for c in chars:
    if dic[c] != count:
        ans = swap[count]
        break
    count += 1
if count <= 25:
    print(swap[count])
else:
    print(ans)

Solution (Python):
s=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']
ss=sorted(s)
for i in alp:
    if i not in ss:
        print(i)
        break
else:
    print('None')

Solution (Python):
import sys

s = input()

alphabet = [0]*26

for i in range(len(s)):
    num_alphabet = ord(s[i])
    alphabet[num_alphabet - 97] = 1

index = -1
for i in range(len(alphabet)):
    if alphabet[i] == 0:
        index = i
        break

print("None") if index == -1 else print(chr(index+97))

Solution (Python):
s = input()
ans_list = [0] * 26

for i in s:
    i = ord(i) - 97
    ans_list[i] += 1

for i, s in enumerate(ans_list):
    if s==0:
        print(chr(i+97))
        exit()

print('None')

Solution (Python):
s = input(); f = 0
words = ['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(words)):
    if words[i] not in s:
        print(words[i])
        f = 1
        break
    
if f == 0:
    print('None')

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

ans = "None"
for i in range(97, 97+26):
    if not chr(i) in s:
        ans = chr(i)
        break

print(ans)

Solution (Python):
alph = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]
s = list(input())
ans = 100
for i in range(26):
    c = 0
    for j in s:
        if alph[i] == j:
            c = 1
            break
    if c == 0:
        ans = i
        break
if ans == 100:
    print("None")
else:
    print(alph[ans])

Solution (Python):
import string

S = input()

flag = False
for l in string.ascii_lowercase:
    if l not in S:
        output = l
        flag = True
        break

if flag:
    print(output)
else :
    print('None')

Solution (Python):
S = list(set(input()))
S.sort()
for i in range(0x61,0x7b):
    if chr(i) not in S:
        print(chr(i))
        exit()
print('None')

Solution (Python):
str = input()
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','aa']
i = 0
while abc[i] in str:
    if i < 26:
        i += 1
    else:
        break

if i < 26:
    print(abc[i])

else:
    print("None")

Solution (Python):
S = list(input())
C = ['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.sort()
set(S)
for c in C:
    if c in(S):
        if c == "z":
            print('None')
        continue
    else:
        print(c)
        break

Solution (Python):
s = list(input())

ans = 'None'
t = []
for i in range(len(s)):
  t.append(ord(s[i]))
for i in range(97, 123):
  if not i in t:
    ans = chr(i)
    break
print(ans)

Solution (Python):
s=sorted(set(input()))
test="abcdefghijklmnopqrstuvwxyz"
for i in range(len(test)):
    if (s[i]!=test[i]):
        print(test[i])
        break
    if (s[i]==test[i] and i==len(s)-1 and i!=len(test)-1):
        print(test[i+1])
        break
else:
    print("None")

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

T=[0]*26
ans=0

for i in range(N):
    T[ord(S[i])-97]+=1

for j in range(26):
    if T[j]==0:
        ans=chr(j+97)
        break

print("None" if ans==0 else ans)

Solution (Python):








def resolve():
    s=list(input())










    def moji_list(*args):
        moji = []
        for i in range(len(args)):
            moji.extend([chr(j) for j in range(args[i][0], args[i][1])])
        return moji

    lowercase = moji_list((97,123))

    print(min(set(lowercase)-set(s) or ['None']))

resolve()

Solution (Python):








def resolve():
    s=list(input())

    
    
    
    
    
    

    def moji_list(*args):
        moji = []
        for i in range(len(args)):
            moji.extend([chr(j) for j in range(args[i][0], args[i][1])])
        return moji

    lowercase = moji_list((97,123))

    for i in s:
        if i in lowercase:
            lowercase.remove(i)
    print(lowercase[0] if len(lowercase)!=0 else 'None')

resolve()

Solution (Python):








def resolve():
    s=list(input())
    lowercase = list('abcdefghijklmnopqrstuvwxyz')

    for i in s:
        if i in lowercase:
            lowercase.remove(i)
    print(lowercase[0] if len(lowercase)!=0 else 'None')

resolve()

Solution (Python):
s = input()
li = []
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 x in alf:
    if x not in s:
        li.append(x)
if li == []:
    print("None")
else:
    print(min(li))

Solution (Python):
S=input()
words=[a for a in S]
arufa=[chr(i) for i in range(97,123)]
for word in words:
    if word in arufa:
        arufa.remove(word)
if arufa==[]:
    print('None')
else:
    print(arufa[0])

Solution (Python):
s = sorted(list(set(input())))
alpha = list('abcdefghijklmnopqrstuvwxyz')
for i in alpha:
    if i not in s:
        print(i)
        break
else:
    print('None')

Solution (Python):
import string
alphabet = [chr(i) for i in range(97, 97+26)]
s = set(input())
result = set(alphabet) - s
result = sorted(list(result))
if len(result) == 0:
  print("None")
else:
  print(result[0])

Solution (Python):
flag=1
a=input()
for i in 'abcdefghijklmnopqrstuvwxyz':
  if i not in a:flag=0;break
print('None'if flag else i)

Solution (Python):
import sys

d={}
ss=input().strip()
for s in ss:
  d[s]=1

for i in range(ord("a"), ord("z")+1):
  if chr(i) not in d:
    print(chr(i))
    sys.exit()
print("None")

Solution (Python):
import sys

a=ord("a")
z=ord("z")

d={}
ss=input().strip()
for s in ss:
  d[s]=1

for i in range(ord("a"), ord("z")+1):
  if chr(i) not in d:
    print(chr(i))
    sys.exit()
print("None")

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

Solution (Python):
s = input()
base = "abcdefghijklmnopqrstuvwxyz"
L = [i for i in base]
L = set(L)

s = set(s)
ans = list(L-s)

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

Solution (Python):
s = set(list(str(input())))
s1=list(sorted(s))
for i in range(len(s1)+1):
    if not chr(i+97) in s1:
        print(chr(i+97))
        break
    elif chr(i+97)=='z':
        print(None)
        break

Solution (Python):
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=list(input())
s_ = list(set(s))


s.sort()
s_.sort()


        
l=[]
cnt=0
for i in range(len(alp)):
            if s.count(alp[i]):
                        pass
            else:
                        l.append(alp[i])
                        cnt+=1

if cnt==0:
            print('None')
else:
            print(min(l))
exit()

Solution (Python):
strings = str(input())
string_list = list(strings)
string_set = set(string_list)

import string

alpha = list(string.ascii_lowercase)
alpha_set = set(alpha)

ans = (alpha_set - string_set)
ans = list(ans)
ans.sort()

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

Solution (Python):
def main():
    import sys
    
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    
    from itertools import combinations, permutations
    
    from bisect import bisect_left,bisect_right
    from math import floor, ceil
    

    

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


if __name__ == '__main__':
    main()

Solution (Python):
abc=set([chr(ord('a')+i) for i in range(26)])
S=set(input())
ans=sorted(list(abc-S))
if len(ans)==0:
    print('None')
else:
    print(ans[0])

Solution (Python):
abc=set([chr(ord('a')+i) for i in range(26)])
S=set(input())
ans=sorted(list(abc.difference(S)))

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

Solution (Python):
s = sorted(set(list(str(input()))))
t = list('abcdefghijklmnopqrstuvwxyz')
ans = ''
for i in range(26):
    if t[i] not in s:
        ans = t[i]
        break
else:
    ans = 'None'
print(ans)

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

Solution (Python):
s = input()
b = [0]*26
for c in s:
  b[ord(c)-ord("a")]+=1
for i,c in enumerate(b):
  if c == 0:
    print(chr(i+ord("a")))
    exit()
print("None")

Solution (Python):

s = list(str(input()))

alph = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
"""
if len(set(s)) >= 26:
    print("None")
    exit()
for i in alph:
    for j in s:
        if not(i in s):
            print(i)
            exit()
"""

check = [False] * 26
for i in s:
    for j in range(26):
        if i == alph[j]:
            check[j] = True
tmp = 0
for i in range(26):
    if check[i] == False:
        print(alph[i])
        exit()
    if check[i]:
        tmp += 1
if tmp == 26:
    print("None")

Solution (Python):

s = list(str(input()))

alph = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
if len(set(s)) >= 26:
    print("None")
    exit()
for i in alph:
    for j in s:
        if not(i in s):
            print(i)
            exit()

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

Solution (Python):
s = sorted(input())
alphabet = 'abcdefghijklmnopqrstuvwxyz'
for i in range(26):
    if not alphabet[i] in s:
        print(alphabet[i])
        break
    if alphabet[i] == 'z':
        print("None")

Solution (Python):
S = input()

S = sorted(S)

S_dict = {}
cnt = 0


for i in range(ord("a"), ord("z") +1):
  S_dict[i] = S.count(chr(i))



ans =None
for i in range(ord("a"), ord("z") +1):
  if S_dict[i] == 0:
    ans = chr(i)
    break
    
print(ans)

Solution (Python):
import sys
input = sys.stdin.readline
import string

S = input().rstrip('\r')
alph = string.ascii_lowercase
S_map = {}
for c in alph:
    S_map[c] = False
for s in S:
    S_map[s] = True
ans = 'None'
for c in alph:
    if not S_map[c]:
        ans = c
        break
print(ans)

Solution (Python):
import sys
input = sys.stdin.readline

def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))

def main():
    mod=10**9+7
    S=set(list(input()))
    T=[]
    for i in range(26):
        T.append(chr(i+97))
    T=set(T)
    ans=list(T-S)

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

main()

Solution (Python):
s = sorted(set(input()))
ans = "None"

for i in "abcdefghijklmnopqrstuvwxyz":
    if i not in s:
        ans = i
        break
        
print(ans)

Solution (Python):


s = sorted(set(input()))
l = "abcdefghijklmnopqrstuvwxyz"
for i in l:
    
    if i not in s:
        print(i)
        break
        
else:
    print("None")

Solution (Python):
al = list("abcdefghijklmnopqrstuvwxyz")
s = list(input())
ans = "None"
for i in al:
  if not i in s:
    ans = i
    break
print(ans)

Solution (Python):
S=input()
alpha=set([i for i in "abcdefghijklmnopqrstuvwxyz"])
ans=alpha-set(list(S))
ans=sorted(ans)
print(ans[0] if len(ans)>0 else 'None')

Solution (Python):

from collections import defaultdict,deque
from heapq import heappush, heappop
from bisect import bisect_left, bisect_right
import sys, random, itertools, math
sys.setrecursionlimit(10**5)
input = sys.stdin.readline
sqrt = math.sqrt
def LI(): return list(map(int, input().split()))
def LF(): return list(map(float, input().split()))
def LI_(): return list(map(lambda x: int(x)-1, input().split()))
def II(): return int(input())
def IF(): return float(input())
def LS(): return list(map(list, input().split()))
def S(): return list(input().rstrip())
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
inf = float('INF')


def solve():
    s = list(set(S()))
    lis = [chr(i) for i in range(ord("a"), ord("z") + 1)]
    for si in s:
        if si in lis:
            lis.remove(si)
        
    lis.sort()
    if lis == []:
        print("None")
    else:
        print(lis[0])
    return



if __name__ == '__main__':
    solve()

Solution (Python):
import numpy as np

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

ans = "None"
for c in t:
    if c not in s:
        ans = c
        break
print(ans)

Solution (Python):
import numpy as np

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

ans = "None"
ls = len(s)
for i in range(ls):
    if s[i] != t[i]:
        ans = t[i]
        break
    elif s[i] == t[i] and i == ls-1 and i < 25:
        ans = t[i+1]
        break
        
print(ans)