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):
S = input()

import string

S = list(sorted(S))
T = string.ascii_lowercase

for t in T:
    if t not in S:
        print(t)
        break
        
else:
    print("None")

Solution (Python):
from string import ascii_lowercase as a
s = set(input())
for c in a:
    if c not in s:
        print(c)
        break
else:
    print('None')

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

def main():
    S = input().strip()
    ch = "abcdefghijklmnopqrstuvwxyz"
    check = [False] * len(ch)
    for c in S:
        for i in range(len(ch)):
            if c == ch[i]:
                check[i] = True
    
    ans = "None"
    for i in range(len(ch)):
        if not check[i]:
            ans = ch[i]
            break
    print(ans)


if __name__ == "__main__":
    main()

Solution (Python):
S = set(map(str, (input())))
s = list(S)
s.sort()
alphabet = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
for i in range(len(s)):
    alphabet.remove(s[i])

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

Solution (Python):
S = set(input())
import string
letters=string.ascii_lowercase
S^=set(letters)
if len(S) == 0:
    print('None')
else:
    print(sorted(S)[0])

Solution (Python):
S = input().strip()
for c in 'abcdefghijklmnopqrstuvwvyz':
  if c not in S:
    print(c)
    exit()
print('None')

Solution (Python):
s=input()
for i 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 (i in s)!=True:
        print(i)
        exit()
print('None')

Solution (Python):
import sys
s = sorted(input())
a = ord('a')
for j in range(26):
    b = a
    for i in s:
        if a == ord(i):
            a += 1
            break
    if a == b:
        print(chr(a))
        sys.exit()
print('None')

Solution (Python):
l=set(map(chr,range(97,123)))
ans = sorted(l ^ set(input()))
print('None' if len(ans)==0 else ans[0])

Solution (Python):
S = sorted(set([i for i in input()]))
for i in "abcdefghijklmnopqrstuvwxyz":
    if i not in S:
        print(i)
        break
else:print("None")

Solution (Python):
a = 'abcdefghijklmnopqrstuvwxyz'
s = input()
for i in a:
    if i not in s:
        print(i)
        break
else:
    print('None')

Solution (Python):
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 = input()
for i in a:
    if i not in s:
        print(i)
        break
else:
    print('None')

Solution (Python):
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 = set(input())
for i in a:
    if i not in s:
        print(i)
        break
else:
    print('None')

Solution (Python):
arr = [s for s in input()]
alphabet = [s for s in 'abcdefghijklmnopqrstuvwxyz']

arr = sorted(list(set(arr)))

for i in range(len(alphabet)):
  if arr.count(alphabet[i]) == 0:
    print(alphabet[i])
    exit()

print('None')

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

Solution (Python):
from string import*
s =input()
s=sorted(s)
alpha_l =[ascii_lowercase[i] for i in range(0,26)]
n='a'
for x in range(0,26):
	if x == 25 and alpha_l[x] in s:
		n = 'None'
	elif alpha_l[x] in s:
		continue
	else:
		n = alpha_l[x]
		break
print(n)

Solution (Python):
import sys
import copy
import  math
import bisect
from collections import *
from operator import itemgetter
"""
from fractions import gcd
def lcm(x, y):
    return (x * y) // gcd(x, y)
"""
stdin = sys.stdin
ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline()

s = input()
li = [chr(ord('a') + i) for i in range(26)]
for c in s:
    if c in li:
        li.remove(c)
if li:
    print(li[0])
else:
    print('None')

Solution (Python):
import string

S = set(list(input()))

for c in string.ascii_lowercase:
  if c not in S:
    print(c)
    exit()

print('None')

Solution (Python):
s = sorted(set(input()))
abc = [chr(i) for i in range(97,97+26)]

for i in abc:
    if s == abc:
        print('None')
        break
    elif i not in s:
        print(i)
        break

Solution (Python):

import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)

alphabet = 'abcdefghijklmnopqrstuvwxyz'

s = input()
for i in s:
    
    alphabet = alphabet.replace(i, '')
print(alphabet[0] if len(alphabet) > 0 else 'None')

Solution (Python):
s = input()

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

else:
    print(None)

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

Solution (Python):
d=[0]*26
for i in input():
    d[ord(i)-97]+=1
print(chr(97+d.index(0)) if 0 in d else"None")

Solution (Python):
S=input()
for s in 'abcdefghijklmnopqrstuvwxyz':
    if S.count(s)==0:
        print(s)
        exit()
print('None')

Solution (Python):
import string
s = input()

s = sorted(set(s))
moji = [chr(i) for i in range(ord('a'), ord('z')+1)]



def b():
    for i in range(len(moji)):
        if i > len(s)-1 or moji[i] != s[i]:
            return moji[i]
    return "None"

print(b())

Solution (Python):
s = input()
a = "abcdefghijklmnopqrstuvwxyz"
diff = sorted(set(a) ^ set(s))
if diff == []:
  print("None")
else:
  print(diff[0])

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

Solution (Python):
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']
L = [0 for i in range(26)]
S = input()
for s in S:
  L[ABC.index(s)]+=1
f = True
for i in range(26):
  if L[i] == 0:
    f = False
    print(ABC[i])
    break
if f:
  print("None")

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

Solution (Python):
S=list(input())
all=['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 s in all:
  if s not in S:
    print(s)
    exit()
print('None')

Solution (Python):
import string
S = input()
al = string.ascii_lowercase
for x in al:
    if x not in S:
        print(x)
        break
else:
    print("None")

Solution (Python):
s = input()
s_num = [ord(s[i]) for i in range(len(s))]
s_num = set(sorted(list(s_num)))

for i in range(ord('a'), ord('z')+2):
  if i == ord('z')+1:
    print('None')
  elif i not in s_num:
    print(chr(i))
    break

Solution (Python):
import string
S = input()
al = string.ascii_lowercase
for x in al:
    if x not in S:
        print(x)
        break
else:
    print("None")

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

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

Solution (Python):
S = input()

T = list('abcdefghijklmnopqrstuvwxyz')

for s in S:
    if s in T:
        T.remove(s)
if not T:
    print('None')
else:
    print(T[0])

Solution (Python):
a = set("abcdefghijklmnopqrstuvwxyz")
a -= set(input())
if a: print(sorted(list(a))[0])
else: print("None")

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

Solution (Python):
L = "abcdefghijklmnopqrstuvwxyz"
for i in set(list(input())):
    L = L.replace(i, "")
if L == "":
    print("None")
else:
    print(L[0])

Solution (Python):
L = "".join([chr(i) for i in range(97, 97 + 26)])
for i in set(list(input())):
    L = L.replace(i, "")
if L == "":
    print("None")
else:
    print(L[0])

Solution (Python):
L = "".join([chr(i) for i in range(97, 97 + 26)])
for i in list(input()):
    L = L.replace(i, "")
if L == "":
    print("None")
else:
    print(L[0])

Solution (Python):
s = set(input())
alpha = "abcdefghijklmnopqrstuvwxyz"
f = False
ans = ""
for i in alpha:
    if not i in s:
        f = True
        ans = i
        break
if f:
    print(ans)
else:
    print("None")

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 = input()
s = set(s)
if len(s)==len(alp):
    print("None")
else:
    s = sorted(s)
    s = list(s)
    for i in alp:
        if i not in s:
          print(i)
          break

Solution (Python):


import string

S = input()

set_s = set(S)
for c in string.ascii_lowercase:
    if c not in set_s:
        print(c)
        exit()
else:
    print('None')

Solution (Python):
def main():
    sc = set(list(input()))
    for c in "abcdefghijklmnopqrstuvwxyz":
        if c not in sc:
            return c
    return "None"



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

Solution (Python):
letters = 'abcdefghijklmnopqrstuvwxyz'
ans = sorted(set(letters) ^ set(input()))
print('None' if len(ans) == 0 else ans[0])

Solution (Python):
s = sorted(list(set(input())))
lst = 'abcdefghijklmnopqrstuvwxyz'
flag = False
for i in lst:
    if i not in s:
        flag = True
        print(i)
        break
if flag == False:
    print('None')

Solution (Python):
import sys
s = sys.stdin.readline().rstrip()
num = [0 for i in range(ord("z")-ord("a")+1)] 
for i in range(len(s)):
    num[ord(s[i])-ord("a")] += 1
for i in range(26):
    if num[i] == 0:
        print(chr(i+ord("a")))
        break
else:
    print("None")

Solution (Python):


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


for c in list("abcdefghijklmnopqrstuvwxyz"):
    if c in s:
        pass
    else:
        print(c)
        exit(0)

print("None")

Solution (Python):
S=input()
alphabet=[chr(x) for x in range(ord("a"),ord("z")+1)]
A={x: 0 for x in alphabet}
for s in S:
    A[s]+=1
for c in alphabet:
    if A[c]==0:
        print(c)
        exit()
else:
    print("None")

Solution (Python):
s=list(input())
t=[ord(si) for si in s]
for i in range(97,124):
  if i==123:
    print('None')
    break
  if not i in t:
    print(chr(i))
    break

Solution (Python):
al = list("abcdefghijklmnopqrstuvwxyz")
S = list(set(list(input())))
S.sort()
for i in S:
  al.remove(i)

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

Solution (Python):
s = input()
sset = set(s)
slist = list(sset)
slist.sort()
char = "abcdefghijklmnopqrstuvwxyz"
flg = False

for i in range(26):
  if len(slist) <= i:
    print(char[i])
    flg = True
    break
  if slist[i] != char[i]:
    print(char[i])
    flg = True
    break

  
if flg == False:
  print("None")

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

Solution (Python):
S = input()
cs = set(S)
for c in "abcdefghijklmnopqrstuvwxyz":
  if not(c in cs):
    print(c)
    exit()
print("None")

Solution (Python):
s= {i for i in input()}
ss = [i for i in "abcdefghijklmnopqrstuvwxyz" if not i in s]
ss.sort()
print(None if not ss else ss[0])

Solution (Python):
s = set(input())
for i in range(26):
    c = chr(i + ord("a"))
    if c not in s:
        print(c)
        exit()
print("None")

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

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 range(len(a)):
	if s.find(a[i]) == -1:
		ans = a[i]
		break
	
print(ans)

Solution (Python):
s=sorted(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']

if s==a:
    print('None')
for i in a:
    if i not in s:
        print(i)
        break

Solution (Python):
s = input()
l = 'abcdefghijklmnopqrstuvwxyz'

for i in range(len(l)):
    if l[i] not in s:
        print(l[i])
        exit()
print('None')

Solution (Python):
S = input()

ret = [0] * 26
for s in S :
    ret[ord(s)-97] = 1
    
for i in range(26) :
    if ret[i] == 0 :
        print(chr(i+97))
        break
else :
    print('None')

Solution (Python):
alphabets = list("abcdefghijklmnopqrstuvwxyz")
appeared = []
S = input()
for c in S:
    if not c in appeared:
        appeared.append(c)
for i in alphabets:
    if not i in appeared:
        print(i)
        exit()
print("None")

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

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

Solution (Python):
S = input()

A = [0 for _ in range(26)]

for s in S:
    A[ord(s) - ord('a')] += 1

for i, a in enumerate(A):
    if a == 0:
        print(chr(i + ord('a')))
        break
else:
    print("None")

Solution (Python):
S = input()

A = [0 for _ in range(26)]

for s in S:
    A[ord(s) - ord('a')] += 1

for i, a in enumerate(A):
    if a == 0:
        print(chr(i + ord('a')))
        break
else:
    print("None")

Solution (Python):


def main(S):
    A = list("abcdefghijklmnopqrstuvwxyz")
    for i in S:
        if i in A:
            A.pop(A.index(i))

    print(A[0]) if A else print("None")
    
if __name__ == '__main__':
    S = input()
    main(S)

Solution (Python):

S = input()
for i in range(ord('a'), ord('z')+1):
    c = chr(i)
    if not c in S:
        print(c)
        exit()

print('None')

Solution (Python):
s = list(input())
abc = list('abcdefghijklmnopqrstuvwxyz')
not_abc = []
cnt = 0

for i in abc:
  if i not in s:
    not_abc.append(i)
    cnt = cnt + 1
  
if cnt == 0:
  print('None')
  
elif cnt >= 1:
  print(sorted(not_abc)[0])

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

Solution (Python):
def find_missing(s):
  letters = set(s)
  for i in range(ord('a'), ord('z') + 1):
    if chr(i) not in letters:
      return chr(i)
    
print(find_missing(input()))

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

Solution (Python):
s=list(input())
s=set(s)
alp="abcdefghijklmnopqrstuvwxyz"
def search():
  for a in alp:
    if not a in s:
      print(a)
      return
  print("None")
  return

search()

Solution (Python):
S = set(list(str(input())))
A = list('abcdefghijklmnopqrstuvwxyz')

if len(S) == len(A):
  print('None')
else:
  for i in A:
    if i not in S:
      print(i)
      break

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



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

for i in range(len(s)):
    if s[i]!=alp[i]:
        print(alp[i])
        break
    if i==len(s)-1:
        if len(s) != len(alp):
            print(alp[i+1])
        else:
            print("None")

Solution (Python):
X = ["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()
s = list(s[i] for i in range(len(s)))
for x in X:
  if x not in s:
    print(x)
    break
else:
  print('None')

Solution (Python):
letters="abcdefghijklmnopqrstuvwxyz"
ans=sorted(set(letters)^set(input()))
print("None" if len(ans)==0 else ans[0])

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

Solution (Python):

S = input()


cand = set('abcdefghijklmnopqrstuvwxyz') - set(S)
if cand:
    res = min(cand)
else:
    res = 'None'


print(res)

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

Solution (Python):
strings = list(input())
alfabet  = 'abcdefghijklmnopqrstuvwxyz'

for i in alfabet:
    if strings.count(i) == 0:
        result = i
        break
else:
    result = "None"

print(result)

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

Solution (Python):
s = set(list(input()))
alf = [chr(i) for i in range(97, 97+26)]
count = 0

for a in alf:
    if a not in s:
        print(a)
        count += 1
        exit()

if count == 0:
    print('None')

Solution (Python):
s = list(input())
alphabet = list('abcdefghijklmnopqrstuvwxyz')
ans_list = list(set(alphabet)-set(s))
if ans_list:
    ans_list.sort()
    print(ans_list[0])
else:
    print('None')

Solution (Python):
s = input()
all = "abcdefghijklmnopqrstuvwxyz"
ans = sorted(set(s)^set(all)) 
print("None" if len(ans) == 0 else ans[0])

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

Solution (Python):
S = input()

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

print('None')

Solution (Python):
import collections
s = collections.Counter(input()).keys()
d = list("abcdefghijklmnopqrstuvwxyz")
for i in d:
    if i not in s:
        print(i)
        exit()
print("None")

Solution (Python):
sl=list(input())
al="abcdefghijklmnopqrstuvwxyz"
l=list(al)
mydic={}
for st in l :
  mydic[st]=0 

for st in sl :
  mydic[st]=mydic[st]+1
ans=[]

for key in mydic.keys() :
  if mydic[key] ==0 :
    ans.append(key)
ans.sort()
if len(ans)==0 :
  print("None")
else :
  print(ans[0])

Solution (Python):

alpha= list("abcdefghijklmnopqrstuvwxyz")

s=input()
for x in alpha:
    if x not in s:
        print(x)
        exit()
    
print("None")

Solution (Python):
S = input()

alphabets = list("abcdefghijklmnopqrstuvwxyz")

ans = "None"

for item in alphabets:
  if item not in S:
    ans = item
    break

print(ans)

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

Solution (Python):
s = input()
ans = set(map(chr,range(ord('a'),ord('z')+1))) - set(s)
print(min(ans) if len(ans)!=0 else 'None')

Solution (Python):
s = input()

ascii_lowercase = 'abcdefghijklmnopqrstuvwxyz'
for c in ascii_lowercase:
    if s.count(c) == 0:
        print(c)
        exit()
print('None')

Solution (Python):
letters="abcdefghijklmnopqrstuvwxyz"
ans=sorted(set(letters)^set(input()))
print("None" if len(ans)==0 else ans[0])

Solution (Python):
s = input()
alphabet = 'abcdefghijklmnopqrstuvwxyz'
rest = sorted(set(alphabet) - set(s))
print('None' if len(rest) == 0 else rest[0])

Solution (Python):
S = input()
alphabet = 'abcdefghijklmnopqrstuvwxyz'
for s in S:
    alphabet = alphabet.replace(s, '')
if not alphabet:
    print('None')
else:
    print(alphabet[0])

Solution (Python):

nlist = [None] * 150

def main():
    
    stri = input()
    
    for i in range(len(stri)):
        ind = ord(stri[i])
        nlist[ind] = 1
    
    for i in range(len(nlist)):
        if nlist[i] == None and (i > 96 and i<123) :
            print(str(chr(i)))
            return
    print("None")

if __name__== "__main__" : main()

Solution (Python):
S = list(input())
abc = list("abcdefghijklmnopqrstuvwxyz")
table = []
for s in abc:
  if s not in S:
    table.append(s)
table.sort()
print(table[0] if len(table) > 0 else "None")

Solution (Python):
ANS = sorted({chr(i) for i in range(97, 123)} - set(input()))
print(ANS[0] if ANS else 'None')

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

s = input().strip()
a = [c for c in "abcdefghijklmnopqrstuvwxyz"]
for c in s:
    if c in a:
        a.remove(c)
if len(a) == 0:
    print("None")
else:
    print(a[0])

Solution (Python):
S = input()

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

for i in range(len(S)):
  if S[i] in li:
    li.remove(S[i])
print (li[0] if len(li) != 0 else "None")

Solution (Python):
alpha_set = set([chr(i) for i in range(97,97+26)])
s = set(input())
diff = list(alpha_set-s)
if len(diff)==0:
  print("None")
else:
  diff.sort()
  print(diff[0])

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

Solution (Python):
S = input()
S = sorted(S)
i = 0
if S[0] != "a":
    print("a")
    exit(0)
while i<len(S)-1:
    if ord(S[i]) == ord(S[i+1]) or ord(S[i]) == ord(S[i+1])-1:
        i += 1
    else:
        print(chr(ord(S[i])+1))
        exit(0)

if S[-1] == "z":
    print("None")
else:
    print(chr(ord(S[i])+1))

Solution (Python):
import sys
s=input()
l="abcdefghijklmnopqrstuvwxyz"
for i in range(len(l)): 
    if l[i] in s: 
        continue
    else:
        print(l[i])
        sys.exit()
print("None")

Solution (Python):
S = list(input())
B = list('abcdefghijklmnopqrstuvwxyz')
D = {}
tmp = 0
for i in range(len(B)):
    D[B[i]] = 0
for i in S:
    D[i] += 1
for i in B:
    if D[i] == 0:
        print(i)
        break
else:
    print('None')

Solution (Python):
from string import ascii_lowercase
s = input()

d = set([s[i] for i in range(len(s))])
ans = "None"
for c in ascii_lowercase:
    if c not in d:
        ans = c
        break

print(ans)

Solution (Python):
S = input()
alpha = [chr(ord('a') + i) for i in range(26)]
n=0
c=-1
while c == -1 and n < 26:
  if not alpha[n] in S:
    c = n
    break
  n+=1
if c == -1:
  print('None')
else:
  print(alpha[n])

Solution (Python):
s=input()
for c in 'abcdefghijklmnopqrstuvwxyz':
  if not c in s:
    print(c)
    break
else:
  print('None')

Solution (Python):
import string
S = input()
for s in string.ascii_lowercase:
    if s not in S:
        print(s)
        break
else:
    print('None')

Solution (Python):
s = input()
t = set()
for i in range(len(s)):
  t.add(s[i])
o = list(t)
o.sort()
u = 'qwertyuiopasdfghjklzxcvbnm'
v = []
for i in range(len(u)):
  v.append(u[i])
v.sort()
now = 0
if len(o) == 26:
  print('None')
else:
  for i in range(26):
    if i >= len(t):
      print(v[i])
      break
    elif o[i] == v[i]:
      now += 1
    else:
      print(v[now])
      break

Solution (Python):
str = input()
n = [0 for i in range(26)]

for j in range(len(str)):
    for i in range(26):
        if ord(str[j]) == ord('a')+i: n[i] += 1

check_flag = 0
for i in range(26):
    if check_flag==0 and n[i] == 0:
        check_flag = 1
        print(chr(97+i))
        break

if check_flag == 0: print('None')

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"]
c = 0
for i in ls:
  if i in s:
    c += 1
  else:
    print(i)
    break
    
if c >= 26:
  print("None")

Solution (Python):
ans = sorted({chr(i) for i in range(97, 123)} - set(input()))
print(ans[0] if ans else 'None')

Solution (Python):
import itertools
s = input()
cnt = ord('a')
for k, _ in itertools.groupby(sorted(s)):
  if not cnt == ord(k):
    break
  cnt += 1
print([chr(cnt), 'None'][cnt>ord('z')])

Solution (Python):
text = input()
alphabet = 'abcdefghijklmnopqrstuvwxyz'

for s in text:
    alphabet = alphabet.replace(s, '')

if alphabet is '':
    print('None')
else:
    print(alphabet[0])

Solution (Python):
diff = set(chr(ord("a") + i) for i in range(26)) - set(input().rstrip("\n"))

print((list(sorted(diff))+["None"])[0])

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


S = list(input())

alphabets = list('abcdefghijklmnopqrstuvwxyz')
for alphabet in alphabets:
    if alphabet in S:
        continue
    else:
        print(alphabet)
        sys.exit()

print('None')

Solution (Python):
a = list("abcdiefhijklmnopqrstuvwxyz")
s = list(input())
for i in a:
    if i not in s:
        print(i)
        exit()
print("None")

Solution (Python):
s = input()
abc = {"a":0,"b":0,"c":0,"d":0,"e":0,"f":0,"g":0,"h":0,"i":0,"j":0,"k":0,"l":0,"m":0,"n":0,"o":0,"p":0,"q":0,"r":0,"s":0,"t":0,"u":0,"v":0,"w":0,"x":0,"y":0,"z":0}
for i in range(len(s)):
    abc[s[i]]+=1
alle = True
for i in abc:
    if abc[i] == 0:
        print(i)
        alle = False
        break
if alle:
    print("None")

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

s_sorted = sorted(set(s))
alpha_dict = {chr(a):0 for a in range(ord('a'), ord('z')+1)}


def getKeyFromValue(d, val):
    keys = [k for k, v in d.items() if v == val]
    keys = sorted(keys)
    if keys:
        return keys[0]
    else:
        return 'None'

for i in range(len(s_sorted)):
    alpha_dict[s_sorted[i]] += 1

print(getKeyFromValue(alpha_dict, 0))

Solution (Python):
import string
abc = list(string.ascii_lowercase)

s = input()
flag = 1

for i in abc:
    if i not in s:
        print(i)
        flag = 0
        break
if flag:
    print("None")

Solution (Python):
s = input()
s = ''.join(list(sorted(set(s))))
a = 'abcdefghijklmnopqrstuvwxyz'
if len(s) == 26:
  print('None')
else:
  for i in range(len(s)):
    if a[i] != s[i]:
      print(a[i])
      break
    if i == len(s)-1:
      print(a[i+1])

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

Solution (Python):
import string
letters=set(string.ascii_lowercase)
S=set(input())
print(min(letters-S or ["None"]))

Solution (Python):
s =input()
ab = [chr(97+i) for i in range(26)]
res = 'None'
for i in ab:
    if i not in s:
        res = i
        break
print(res)

Solution (Python):
import string
S = input()
al = string.ascii_lowercase

for a in al:
    if a not in S:
        print(a)
        break
else:
    print('None')

Solution (Python):
import sys
s = input()
s_set = set(s)
alpha = 'abcdefghijklmnopqrstuvwxyz'
for i in alpha:
    if i not in s_set:
        print(i)
        sys.exit()
print('None')

Solution (Python):
s = list(set(list(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"]
li = []
for i in range(len(a)):
  if a[i] not in s:
    li.append(a[i])
if len(li) == 0:
    print("None")
else:
    print(min(li))

Solution (Python):

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

Solution (Python):
import string
s=set(list(input()))
if len(s)==26:
  print("None")
else:
  a=set(list(string.ascii_lowercase))
  print(sorted(list(a-s))[0])

Solution (Python):
S = input()
hantei = 0

serch = ('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','y','z')

for i in range(0,25):
    if S.count(serch[i]) == 0 :
        hantei = 1
        print(serch[i])
        break

if hantei == 0:
    print('None')

Solution (Python):
s = input()
l = [chr(ord("a")+i) for i in range(26)]
arr = {}
for i in l:
  arr[i] = False
for j in s:
  arr[j] = True
for k, v in sorted(arr.items()):
  if v == False:
    print(k)
    exit()
print("None")

Solution (Python):
S = input()

alp = 'abcdefghijklmnopqrstuvwxyz'
for i in alp:
    if not i in S:
        print(i)
        exit()
print('None')

Solution (Python):
S = input()

alp = 'abcdefghijklmnopqrstuvwxyz'
for i in alp:
    if i not in S:
        print(i)
        exit()
print('None')

Solution (Python):
a = "abcdefghijklmnopqrstuvwxyz"
a = list(a)
s = set(input())
c = 0
for i in a:
    if not i in s:
        c = 1
        print(i)
        break
if c == 0:
    print("None")

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

Solution (Python):

import sys
from collections import Counter
INF = float("inf")


def solve(S: str):
    counter = Counter(S)
    for i in range(ord("a"), ord("z")+1):
        if counter[chr(i)] == 0:
            break
    else:
        print("None")
        return
    print(chr(i))

    return


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 = input()
a = 'abcdefghijklmnopqrstuvwxyz'
ans = 'None'
for c in a:
  if s.find(c) < 0:
    ans = c
    break
print(ans)

Solution (Python):
S = input()

D = 'abcdefghijklmnopqrstuvwxyz'
temp = D

for i in S:
    res = ''
    for j in temp:
        if i != j:
            res += j
    temp = res

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

Solution (Python):
s = input()
l_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"]
ans = [0]*26
for i in range(26):
	if l_alph[i] in s:
		ans[i] = 1
for i in range(26):
	if not ans[i]:
		print(l_alph[i])
		quit()
print("None")

Solution (Python):
s = input()

sLst = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n',\
        'o','p','q','l','s','t','u','v','w','x', 'y', 'z']
ansLst = []

for i in sLst:
    if s.count(i) == 0:
        ansLst.append(i)

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

Solution (Python):
if __name__ == '__main__':
    S = input()

    complement_S = list(set([chr(i) for i in range(ord('a'), ord('z')+1)]) - set(list(S)))

    if len(complement_S) == 0:
        print("None")
    else:
        print(min(complement_S))

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

Solution (Python):
S = input()
str = "abcdefghijklmnopqrstuvwxyz"
l1 = list(str)
l2 = list(S)
l3 = list(set(l1)-set(l2))
l3.sort()
if len(l3)==0:
    print("None")
else:
    print(l3[0])

Solution (Python):
s = input()
s = [ord(ss) for ss in s]
flag = []
for i in range(ord('a'), ord('z')+1):
  if i in s:
    flag.append(i)
if len(set(flag)) == 26:
  print('None')
else:
  for i in range(ord('a'), ord('z')+1):
    if i not in flag:
      print(chr(i))
      break

Solution (Python):
import string
S = input()
S = sorted(S)
ans = 'None'
char = [chr(i) for i in range(97, 97+26)]
for i in char:
    if i not in S:
        ans = i
        break
print(ans)

Solution (Python):
d = set("abcdefghijklmnopqrstuvwxyz") - set(input())
if d:
  print(sorted(d)[0])
else:
  print(None)