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

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

Solution (Python):
s = input()
az = [0]*26
for c in s:
    az[ord(c)-ord("a")]=1
if sum(az)==26:
    print("None")
else:
    print(chr(ord("a")+az.index(0)))

Solution (Python):
S = sorted(list(set(input())))
Alphabet = "abcdefghijklmnopqrstuvwxyz"
for i in Alphabet:
    if i not in S:
        print(i)
        exit()
print("None")

Solution (Python):
s = input()
s_list = []
alphabet_list = [chr(i) for i in range(97, 123)]
count = 0
exit = 0

for i in s:
    s_list.append(i)

for j in range(len(alphabet_list)):
    alphabet = alphabet_list[j]
    count = 0
    for k in range(len(s_list)):
        if alphabet == s[k]:
            count += 1
    if count == 0:
        print(alphabet)
        break
    else:
        exit += 1

if exit == len(alphabet_list):
    print("None")

Solution (Python):
s = input()
def is_alpha(s):
  if len(set(s)) == 26:
    return 'None'
  al = {chr(i):0 for i in range(97, 97+26)}
  for i in s:
    al[i] +=1
  result = []
  for k, v in al.items():
    if v == 0:
      result.append(k)
  return min(result)


print(is_alpha(s))

Solution (Python):




s = input()

cl = ["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 = None
for i in range(len(cl)):
    exflg = False
    for j in range(len(s)):
        if s[j] == cl[i]:
            exflg = True
            break
    if exflg == False:
        ans = cl[i]
        break


print(ans)

Solution (Python):
X = set()
for x in input():
  X.add(x)
X = sorted(X)
codeA = "a".encode("sjis")[0]
codes = [bytes([codeA + i]).decode("sjis") for i in range(26)]
codes.append("None")
print(codes[sum([1 for i, x in enumerate(X) if x == codes[i]])])

Solution (Python):
X = set()
for x in input():
  X.add(x)
X = sorted(X)
c = bytes(["a".encode("sjis")[0] + sum([1 for i, x in enumerate(X) if x.encode("sjis")[0] == "a".encode("sjis")[0] + i])]).decode("sjis")

if c.encode("sjis")[0] > "z".encode("sjis")[0]:
  c = "None"

print(c)

Solution (Python):
from string import ascii_lowercase
s = input()
for chr in ascii_lowercase:
    if not chr in s:
        print(chr)
        exit()
print('None')

Solution (Python):
s = input()
alist = [chr(i) for i in range(97,97+26)]
count = 0
for j in alist:
    if j not in s:
        print(j)
        break
    else:
        count += 1
if count == 26:
    print(None)

Solution (Python):
from sys import exit, stdin
from string import ascii_lowercase
s = set(stdin.readline().rstrip())
ansl = list(set(ascii_lowercase)-s)
ansl.sort()
if ansl:
    print(ansl[0])
else:
    print('None')

Solution (Python):
s=input()
alp='abcdefghijklmnopqrstuvwxyz'
for i in range(26):
  if alp[i] not in s:
    print(alp[i])
    break
else:
  print('None')

Solution (Python):
s = list(sorted(set(input())))
dic = list("abcdefghijklmnopqrstuvwxyz")
for i in s:
        dic.remove(i)
if not dic:
        print("None")
else:
        print(min(dic))

Solution (Python):
alphabet = [chr(i) for i in range(97, 97 + 26)]
s = input()
for c in alphabet:
    if c not in s:
        print(c)
        exit()
print('None')

Solution (Python):
s = input()
ss = set()
for c in s:ss.add(c)
for b in 'abcdefghijklmnopqrstuvwxyz':
    if not b in ss:
        print(b)
        break
else:print('None')

Solution (Python):
S = input()
komoji = "abcdefghijklmnopqrstuvwxyz"
for char in komoji:
    if S.count(char) == 0:
        print(char)
        exit()
print("None")

Solution (Python):
s=list(input())
s=list(set(s))
s.sort()
key='A'
for i in range(len(s)-1):
    if s[i+1]!=chr(ord(s[i])+1):
        key=chr(ord(s[i])+1)
        break
            
if len(s)==1:
    print(chr(ord(s[0])+1))
elif len(s)==26:
    print('None')
elif key!='A' and s[0]=="a": print(key)
elif key!='A' and s[0]!="a": print("a")
else: print(chr(ord(s[len(s)-1])+1))

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

a = set(map(chr, range(ord('a'), ord('z')+1)))
s = set(input())
ans = a-s
print(min(ans) if ans else 'None')

Solution (Python):
S = input()
for c in 'abcdefghijklmnopqrstuvwxyz':
  if S.count(c) == 0:
    print(c)
    break
else:
    print('None')

Solution (Python):
s = input()
for i in "abcdefghijklmnopqrstuvwxyz":
    if i not in s:
        print(i)
        exit()

print("None")

Solution (Python):
S = set(input())

for code in range(ord('a'), ord('z')+1):
    if chr(code) not in S:
        print(chr(code))
        break
else:
    print('None')

Solution (Python):
S = 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"] 
B = [0]*26
flag = -1

for i in range(len(S)):
  
  for j in range(len(A)):
    if S[i] == A[j]:
      B[j] += 1
      break
  
  if i == len(S):
    break

for k in range(len(B)):
  if B[k] == 0:
    print(A[k])
    flag = 1
    break
    
if flag == -1:
  print("None")

Solution (Python):
s = input()

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

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

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

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

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

Solution (Python):
import string

s_lower_alpha = set(string.ascii_lowercase)
s_S = set(input())
ret = sorted(list(s_lower_alpha - s_S))

if len(ret) > 0:
    print(ret[0])
else:
    print('None')

Solution (Python):

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')

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

Solution (Python):
s=set(list(input()))
a=set('abcdefghijklmnopqrstuvwxyz')
print('None' if s==a else min(s^a))

Solution (Python):


def solve():
    S = input()
    S = list(S)
    S.sort()

    
    import copy
    tmpS = copy.deepcopy(S)
    S = []
    S.append(tmpS[0])
    for i in range(1, len(tmpS)):
        if S[-1] == tmpS[i]:
            continue
        S.append(tmpS[i])

    ans = "a"
    for moji in S:
        if ans == moji:
            ans = chr(ord(ans)+1)
            continue
        
        break
    if ans == "{":
        print("None")
    else:
        print(ans)


if __name__ == "__main__":
    solve()

Solution (Python):
import sys
S = input()
alphabet = [chr(_) for _ in range(ord("a"), ord("z") + 1)]
l_unique = set(list(S))
for i in alphabet:
    if i not in l_unique:
        print(i)
        sys.exit()
else:
    print("None")

Solution (Python):

import string
S = list(input())
alf = [False]*26
for s in S:
    alf[ord(s)-ord("a")] = True

for a in range(len(alf)):
    if not alf[a]:
        print(chr(a+97))
        break
        
    elif a == len(alf)-1:
        print("None")

Solution (Python):
S=list(input())
S=set(S)
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=list(A-S)
B.sort()
if len(B)>0:
    print(B[0])
else:
    print('None')

Solution (Python):
S = input()

candidates = {
    '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'
} - set(S)
if len(candidates) == 0:
    print('None')
    exit(0)
candidates = list(candidates)
candidates.sort()
print(candidates[0])

Solution (Python):
s=set(list(input()))
alpha=list("abcdefghijklmnopqrstuvwxyz")
for i in reversed(range(len(alpha))):
    if alpha[i] in s:
        alpha.pop(i)
if alpha == []:
    print("None")
else:
    print(alpha[0])

Solution (Python):
s = input()
binary = {}
alphabet = "abcdefghijklmnopqrstuvwxyz"
flag = False
for i in alphabet:
    binary[i] = 0
for j in s:
    binary[j] = 1
for k in alphabet:
    if binary[k] == 0:
        print(k)
        break
    if "z" == k:
        print("None")

Solution (Python):
s = set(input())
a_z = {chr(s) for s in range(ord("a"), ord("z")+1)}
s_diff = a_z - s
print(sorted(s_diff)[0] if s_diff else "None")

Solution (Python):
s=str(input())
flag=True
t=[chr(ord('a') + i) for i in range(26)]
for i in range(len(t)):
    if t[i] not in s:
        flag=False
        print(t[i])
        break
    else:
        pass
if flag:
    print("None")

Solution (Python):
xs = set(range(ord("a"),ord("z")+1)) - set(map(ord, input()))
print(chr(min(xs)) if len(xs) else "None")

Solution (Python):
"""
文字列lの？個目が文字列Sに含まれたらansの？個目は0，含まれなかったら1
ansの要素を全部足して0だったら文字列Sにはアルファベットが全て含まれる
range(25)にしていた
これだとiが0~24まで25回しか繰り返していない
"""
s=input()
l="abcdefghijklmnopqrstuvwxyz"
ans=[0]*26
for i in range(26):
    if l[i] not in s:
        ans[i]=1
    else:
        ans[i]=0
if sum(ans[x] for x in range(26))>0:
    print(l[ans.index(1)])
else:
    print("None")

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

Solution (Python):
x = list(input())
a = "abcdefghijklmnopqrstuvwxyz"
res = "None"
for i in range(len(a)):
  if a[i] not in x:
    res = a[i]
    break
print(res)

Solution (Python):
import sys
s=input()
s=set(x for x in s)
for i in range(97,97+26):
    l=chr(i)
    if not l in s:
        print(l)
        sys.exit()
print('None')

Solution (Python):
import string 
L = string.ascii_lowercase
S = list(str(input()))
ans = ''
for l in L:
  if l not in S:
    ans =l
    break
if ans != '':
  print(ans)
else:
  print("None")

Solution (Python):
a='abcdefghijklmnopqrstuvwxyz'
b=list(input())
for i in a:
    if i not in b:
        ans=i
        break
print(i if len(set(b))!=26 else 'None' )

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

Solution (Python):
S = set(input())
ans = list("abcdefghijklmnopqrstuvwxyz")+[None]
for c in S:
    if c in ans:
        ans.remove(c)
print(ans[0])

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

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 = set(sorted(s))

result=list(set(x)-set(S))

result=sorted(result)

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

Solution (Python):
import string

char = string.ascii_lowercase
s = input()

for i in char:
    ans = i
    if s.count(i):
        continue
    else:
        print(ans)
        quit()
print('None')

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

Solution (Python):
l=list("abcdefghijklmnopqrstuvwxyz")
w=list(input())
b=True
for i in l:
  if not(i in w):
    print(i)
    b=False
    break
if b:
  print("None")

Solution (Python):
S=list(input())
a = list("abcdefghijklmnopqrstuvwxyz")
a.append("None")
print([x for x in a if not(x in S)][0])

Solution (Python):
import string


def solve(s):
  asc = string.ascii_lowercase
  for c in asc:
    if c not in s:
      return c


s = str(input())
print(solve(s))

Solution (Python):
S = list(input())
a = list("abcdefghijklmnopqrstuvwxyz")
a.append("None")
print([x for x in a if not(x in S)][0])

Solution (Python):
S = set(input())
for x  in 'abcdefghijklmnopqrstuvwxyz':
    if not x in S:
        print(x)
        exit(0)
print('None')

Solution (Python):
s = input()
for c in "abcdefghijklnmopqrstuvwxyz":
    if not c in s:
        print(c)
        exit()
print(None)

Solution (Python):

def read_input():
    s = input()
    return s

def submit():
    s = read_input()

    char_appear = {}
    for c in s:
        char_appear[c] = 1

    test = 'abcdefghijklmnopqrstuvwxyz'
    for t in test:
        if t not in char_appear.keys():
            print(t)
            return
    print('None')


if __name__ == '__main__':
    submit()

Solution (Python):
import string
import sys
from collections import Counter

s = input()
all = string.ascii_lowercase
rest = list(set(all) - set(s))

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

Solution (Python):
import sys
from collections import Counter

s_set = set(input())
alph = 'abcdefghijklmnopqrstuvwxyz'

for i in alph:
    if not i in s_set:
        print(i)
        sys.exit()

print('None')

Solution (Python):

import string

s = set(input())
lw = set(string.ascii_lowercase)
dif = lw - s
if dif == set():
    print("None")
else:
    print(sorted(list(dif))[0])

Solution (Python):
S = sorted(list(set(input())))
sss = "abcdefghijklmnopqrstuvwxyz"
for s in sss:
    if s not in S:
        print(s)
        exit()
print("None")

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

AL = [chr(i) for i in range(97, 97 + 26)]
f = 0
for al in AL:
    if al not in S:
        f = 1
        break

print(al) if f else print('None')

Solution (Python):
import sys, os

f = lambda:list(map(int,input().split()))
if 'local' in os.environ :
    sys.stdin = open('./input.txt', 'r')

def solve():
    s = input()
    ss = set(s)
    if len(ss) == 26:
        print('None')
    else:
        for i in range(26):
            if chr(ord('a')+i) not in ss:
                print(chr(ord('a')+i))
                return

solve()

Solution (Python):
from functools import reduce
import math

def main():
    
    
    
    

    
    
    
    
    
    

    
    

    
    
    
    
    
    
    
    
    
    INF = float("inf")

    
    MOD = 10**9+7
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    
    
    
    
    S = input().rstrip()
    alphabets = 'abcdefghijklmnopqrstuvwxyz'
    ans = 'None'
    for a in alphabets:
        if S.count(a) < 1:
            ans = a
            break
    print(ans)
    
if __name__ == '__main__':
    main()

Solution (Python):
d = {chr(i) for i in range(ord('a'), ord('z') + 1)} - {c for c in input()}
print('None' if len(d) == 0 else sorted(list(d))[0])

Solution (Python):
d = {chr(i) for i in range(ord('a'), ord('z') + 1)} - {c for c in input()}
print('None' if len(d) == 0 else sorted(list(d))[0])

Solution (Python):
s=set(input())
ab=set([chr(i) for i in range(97,97+26)])
ans=sorted(ab-s)
print('None' if not ans else ans[0])

Solution (Python):
S = input()

for a in 'abcdefghijklmnopqrstuvwxyz':
    if not a in S:
        print(a)
        quit()
print('None')

Solution (Python):

import sys
try:
    from math import gcd
except Exception:
    from fractions import gcd


def solve(S: str):
    res = sorted(list(set([chr(c) for c in range(ord('a'),ord('z')+1)]) - set(S)))
    return 'None' if len(res) == 0 else res[0]

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

if __name__ == '__main__':
    main()

Solution (Python):
s = input()
cnt = [0]*26
for c in s:
    cnt[ord(c)-ord("a")] += 1
ans = "None"
for i in range(26):
    if cnt[i] == 0:
        ans = chr(ord("a")+i)
        break
print(ans)

Solution (Python):
s = input()
n = len(s)
l = list(set(s))
l.sort()
import string
o = 'None'
for v in string.ascii_lowercase:
  if v not in l:
    o = v
    break
print(o)

Solution (Python):
S = input()

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

for x in alphabet:
    if x in S:
        continue
    else:
        print(x)
        exit()

print('None')

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

Solution (Python):
s=set(input());a=[i for i in range(26)if chr(i+97)not in s];print(chr(min(a)+97)if len(a)>0else '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 range(26):
	if not A[i] in S:
		print(A[i])
		exit()
print("None")

Solution (Python):
import string
alphas = string.ascii_lowercase

S = input()

for al in alphas:
    if al in S:
        continue
    else:
        print(al)
        exit()
print("None")

Solution (Python):
alpha = "abcdefghijklmnopqrstuvwxyz"
S = input()
flag = True
for i in alpha:
  if i in S:
    pass
  else:
    print(i)
    flag = False
    break
    
if flag:
  print("None")

Solution (Python):

import sys
s=list(str(input()))
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"]

for i in range(len(x)):
    if x[i] in s:
        pass
    else:
        print(x[i])
        sys.exit()


print("None")

Solution (Python):
l=[chr(ord("a")+i) for i in range(26)]
s=set(input())
for i in s:
    l.remove(i)
print(l[0] if len(l)>0 else "None")

Solution (Python):
l=[chr(ord("a")+i) for i in range(26)]
s=set(input())
for i in s:
    l.remove(i)
print(l[0] if len(l)>0 else "None")

Solution (Python):
import sys
S = input()
alp = 'abcdefghijklmnopqrstuvwxyz'
for i in alp:
    if i not in S:
        print(i)
        sys.exit()

print('None')

Solution (Python):
S = input()

atoz = 'abcdefghijklmnopqrstuvwxyz'
ans = 'None'
for al in atoz:
    if al in S:
        continue
    else:
        ans = al
        break

print(ans)

Solution (Python):

import copy
import random
import bisect 
import math


S = str(input())


all = list("abcdefghijklmnopqrstuvwxyz")
all.sort()
for i in range(len(S)):
    if S[i] in all:
        all.remove(S[i])

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

Solution (Python):
alfabets = [chr(i) for i in range(97,97+26)]
a = []
s = input()
for i in s :
    a += i
s1 = set(alfabets)
s2 = set(a)
aaa = s1 - s2
alfabets = list(aaa)
alfabets.sort()
if alfabets == [] :
    print('None')
else : 
    print(alfabets[0])

Solution (Python):
S = input()
check = [False] * 26
for i in S:
    check[ord(i)-ord('a')] = True

ans = 'None'
for i in range(len(check)):
    if check[i]:
        continue
    else:
        ans = chr(i+ord('a'))
        break
print(ans)

Solution (Python):
import string

s = input()

left_character_set = set(string.ascii_lowercase) - set(s)
print(chr(min(ord(c) for c in left_character_set)) if len(left_character_set) > 0 else "None")

Solution (Python):
chars=list(input())
d_unique=list(set(chars))

if len(d_unique)==26:
    print("None")
elif "a" not in d_unique:
    print("a")
elif "b" not in d_unique:
    print("b")
elif "c" not in d_unique:
    print("c")
elif "d" not in d_unique:
    print("d")
elif "e" not in d_unique:
    print("e")
elif "f" not in d_unique:
    print("f")
elif "g" not in d_unique:
    print("g")
elif "h" not in d_unique:
    print("h")
elif "i" not in d_unique:
    print("i")
elif "j" not in d_unique:
    print("j")
elif "k" not in d_unique:
    print("k")
elif "l" not in d_unique:
    print("l")
elif "m" not in d_unique:
    print("m")
elif "n" not in d_unique:
    print("n")
elif "o" not in d_unique:
    print("o")
elif "p" not in d_unique:
    print("p")
elif "q" not in d_unique:
    print("q")
elif "r" not in d_unique:
    print("r")
elif "s" not in d_unique:
    print("s")
elif "t" not in d_unique:
    print("t")
elif "u" not in d_unique:
    print("u")
elif "v" not in d_unique:
    print("v")
elif "w" not in d_unique:
    print("w")
elif "x" not in d_unique:
    print("x")
elif "y" not in d_unique:
    print("y")
elif "z" not in d_unique:
    print("z")

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

Solution (Python):
S=input()
d=[chr(i) for i in range(97,97+26)]
d.sort(reverse=True)
ans='None'
for j in d:
    if S.find(j)==-1:
        ans=j
print(ans)

Solution (Python):
*S, = sorted(set(input()))
for i, s in enumerate(S):
	lowest = ord(s) - 1
	if ord("a") <= lowest and chr(lowest) not in S:
		print(chr(lowest))
		break
else:
	if ord(S[-1]) < ord("z"):
		print(chr(ord(S[-1])+1))
	else:
		print("None")

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

Solution (Python):
s=input()
l=len(s)
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']
ans=[0]*26
for i in range(l):
  for j in range(26):
    if s[i]==alpha[j]:
      ans[j]+=1
for i in range(26):
  if ans[i]==0:
    print(alpha[i])
    break
  if i==25:
    print('None')

Solution (Python):

import sys
import string

alphabets = string.ascii_lowercase
s = input()

for i in alphabets:
    if i not in s:
        print(i)
        sys.exit()

print("None")

Solution (Python):
S=list(input())
alphabet= "abcdefghijklmnopqrstuvwxyz"
flag=True
for i in alphabet:
    if i not in S:
        print(i)
        flag=False
        break
    else:
        continue
if flag==True:
    print("None")
else:
    exit

Solution (Python):
s=input()
alphabet=sorted(map(chr,range(97,123)))
print("None" if set(alphabet)==set(list(s)) else sorted(set(alphabet)-set(list(s)))[0])

Solution (Python):
alphabet='abcdefghijklmnopqrstuvwxyz'
S=input()
def findabc():
    for i in alphabet:
    	if i not in S:return i
print(findabc())

Solution (Python):
from collections import defaultdict
import string

S = input()

letters = defaultdict(lambda: False)
for s in S:
    letters[s] = True

ans = 'None'
for l in string.ascii_lowercase:
    if letters[l] == False:
        ans = l
        break
print(ans)

Solution (Python):
import string

s = set(input())
for w in string.ascii_lowercase:
    if w not in s:
        print(w)
        break
else:
    print('None')

Solution (Python):
s = list(input())
s.sort()
abc = 'abcdefghijklmnopqrstuvwxyz'
ans = 'None'

for i in range(26):
	if abc[i] in s:
		continue
	else:
		ans = abc[i]
		break
print(ans)

Solution (Python):
import itertools
from collections import Counter
import bisect

def main():
    s = list(input())
    s = list(set(s))
    s.sort()
    cur = ord('a')
    
    for c in s:
        if cur == ord(c):
            cur = cur + 1
        else:
            print(chr(cur))
            exit()
    if cur == ord('z') + 1:
        print('None')
    else:
        print(chr(cur))

if __name__ == '__main__':
    main()

Solution (Python):
s = sorted(input())
result = ''

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

print(result if result != '' else 'None')

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

dct = {chr(i):0 for i in range(97, 97+26)}
result = ''

for c in s:
    if c in dct:
        dct[c] += 1

for i in range(97, 97+26):
    c = chr(i)
    if c in dct and dct.get(c) == 0:
        result = c
        break

print(result if result != '' else 'None')

Solution (Python):
alp = "abcdefghijklmnopqrstuvwxyz"
for c in list(input()):
    alp = alp.replace(c, "")
print(alp[0] if len(alp) else "None")

Solution (Python):
s = list(input())
alpha = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
for x in s:
    if x in alpha:
        alpha.remove(x)
print(alpha[0] if len(alpha)>0 else "None")

Solution (Python):
import string
S = input()
A = string.ascii_lowercase
ans = list(set(A) - set(S))
ans.sort()
if ans == []:
    print('None')
else:
    print(ans[0])

Solution (Python):
s = input()
is_inS = [0] * 26
for c in s:
    is_inS[ord(c) - 97] = 1

for i in range(26):
    if is_inS[i] == 0:
        print(chr(i+97))
        exit()
print("None")

Solution (Python):
abc=[chr(i) for i in range(97,97+26)]
s=input()
for i in abc:
    if i not in s:
        print(i)
        exit()
print('None')

Solution (Python):
alphabet = {1:"a",2:"b"}
backet = [0]*26
S = input()
for char in S:
    backet[ord(char)-97] = 1
if backet == [1]*26:
    print("None")
else:
    print(chr(backet.index(0)+97))

Solution (Python):
import sys
ns = lambda: sys.stdin.readline().rstrip()
ni = lambda: int(ns())
nm = lambda: map(int, sys.stdin.readline().split())
nl = lambda: list(nm())

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

Solution (Python):
s=input()
a=sorted(set(s))
E="abcdefghijklmnopqrstuvwxyz"
if len(set(a))==26:
  print("None")
else:
  count=0
  for i in range(len(a)):
    if a[i]==E[i]:
      count+=1
    else:
      break
  print(E[count])

Solution (Python):
S = str(input())
ascii_letters = "abcdefghijklmnopqrstuvwxyz"
for letter in ascii_letters:
    if letter not in S:
        print(letter)
        exit()
print("None")

Solution (Python):
S = input()

flag = False
for i in range(97,97 + 26):
    c = chr(i)
    if c not in S:
        print(c)
        flag = True
        break

if not flag:
    print("None")

Solution (Python):
S = input().rstrip()
element = [0]*26
for i in range(len(S)):
    s = ord(S[i]) - ord("a")
    element[s] += 1
zero = element.count(0)
print("None" if zero == 0 else chr(ord("a") + element.index(0)))

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

Solution (Python):
s = input()
found = False
at = "X"
for i in 'abcdefghijklmnopqrstuvwxyz':
    if i not in s:
        at = i
        found = True
        break
if found:
    print(at)
else:
    print("None")

Solution (Python):
s=list(set(input()))
s.sort()
alpha=[chr(i) for i in range(97, 97+26)]
ans='None'
for i in alpha:
    if i not in s:
        ans=i
        break
print(ans)

Solution (Python):
import string
s = str(raw_input())
al = [chr(i) for i in range(97, 97+26)]
opt = list(set(al) - set(list(s)))
opt.sort()
if len(opt) == 0:
	print 'None'
else:
	print opt[0]

Solution (Python):
import sys
S = input()

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

setS = sorted(set(S))
for A in alphabets:
  if A not in setS:
    print(A)
    sys.exit()
  else: continue
print('None')

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

Solution (Python):
import string

S = list(input())

d = set(list(string.ascii_lowercase[:26])) - set(S)
d = list(d)
d = sorted(d)

if len(d)>0:
    print(d[0])
else:
    print('None')

Solution (Python):
s=input()
w=["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 s:
    if x in w:
       w.remove(x)
if w==[]:
    print("None")
else:
    print(w[0])

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

Solution (Python):

s = list(set(input()))
s.sort()
x = list("abcdefghijklmnopqrstuvwxyz")
for i in range(min(len(s),len(x))):
    if s[i] !=x[i]:
        print(x[i])
        break
    if i==25:
        print("None")
        break
    if i+1 == min(len(s),len(x)):
        print(x[i+1])
        break

Solution (Python):
s=input()

moji="abcdefghijklmnopqrstuvwxyz"

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

Solution (Python):
s = input()
x=0
listA = ["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 s.count(listA[i])==0:
    print(listA[i])
    x=1
    break
if x==0:
  print("None")

Solution (Python):
s = list(set(input()))
d = 'abcdefghijklmnopqrstuvwxyz'
for di in d:
    if di not in s:
        print(di)
        exit()
print('None')

Solution (Python):
S = list(input())
str = 'abcdefghijklmnopqrstuvwxyz'
ans = list('abcdefghijklmnopqrstuvwxyz')
for s in str:
  if (s in S):
    ans.remove(s)

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

Solution (Python):



S = input()

ans = 'None'
for i in range(26):
    if chr(i + 97) not in S:
        ans = chr(i + 97)
        break

print(ans)

Solution (Python):


A = 'abcdefghijklmnopqrstuvwxyz'

S = input()

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

Solution (Python):


l = []
A = 'abcdefghijklmnopqrstuvwxyz'

S = input()

for i in A:
    if i not in S:
        l.append(i)
print('None' if len(l) == 0 else min(l))

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

Solution (Python):


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

for i in range(len(t)):
    for j in range(len(s)):
        if t[i] == s[j]:
            break
    else:
        print(t[i])
        break
else:
    print("None")

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

Solution (Python):
import sys

def main():
    input = sys.stdin.readline
    A = list(map(str, input().strip()))
    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',
            'None']

    for a in alph:
        if a not in A:
            return a


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

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