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()

num=[0]*26

for i in range(len(S)):
    if S[i] == "a":
        num[0] +=1
    elif S[i] == "b":
        num[1] +=1
    elif S[i] == "c":
        num[2] +=1
    elif S[i] == "d":
        num[3] +=1
    elif S[i] == "e":
        num[4] +=1
    elif S[i] == "f":
        num[5] +=1
    elif S[i] == "g":
        num[6] +=1
    elif S[i] == "h":
        num[7] +=1
    elif S[i] == "i":
        num[8] +=1
    elif S[i] == "j":
        num[9] +=1
    elif S[i] == "k":
        num[10] +=1
    elif S[i] == "l":
        num[11] +=1
    elif S[i] == "m":
        num[12] +=1
    elif S[i] == "n":
        num[13] +=1
    elif S[i] == "o":
        num[14] +=1
    elif S[i] == "p":
        num[15] +=1
    elif S[i] == "q":
        num[16] +=1
    elif S[i] == "r":
        num[17] +=1
    elif S[i] == "s":
        num[18] +=1
    elif S[i] == "t":
        num[19] +=1
    elif S[i] == "u":
        num[20] +=1
    elif S[i] == "v":
        num[21] +=1
    elif S[i] == "w":
        num[22] +=1
    elif S[i] == "x":
        num[23] +=1
    elif S[i] == "y":
        num[24] +=1
    elif S[i] == "z":
        num[25] +=1
        
ans = num.count(0)

if ans == 0:
    print("None")
else:
    ans1 = num.index(0)
    if ans1 == 0:
        print("a")
    elif ans1 == 1:
        print("b")
    elif ans1 == 2:
        print("c")
    elif ans1 == 3:
        print("d")
    elif ans1 == 4:
        print("e")
    elif ans1 == 5:
        print("f")
    elif ans1 == 6:
        print("g")
    elif ans1 == 7:
        print("h")
    elif ans1 == 8:
        print("i")
    elif ans1 == 9:
        print("j")
    elif ans1 == 10:
        print("k")
    elif ans1 == 11:
        print("l")
    elif ans1 == 12:
        print("m")
    elif ans1 == 13:
        print("n")
    elif ans1 == 14:
        print("o")
    elif ans1 == 15:
        print("p")
    elif ans1 == 16:
        print("q")
    elif ans1 == 17:
        print("r")
    elif ans1 == 18:
        print("s")
    elif ans1 == 19:
        print("t")
    elif ans1 == 20:
        print("u")
    elif ans1 == 21:
        print("v")
    elif ans1 == 22:
        print("w")
    elif ans1 == 23:
        print("x")
    elif ans1 == 24:
        print("y")
    elif ans1 == 25:
        print("z")

Solution (Python):
S = input()
alphabet = 'abcdefghijklmnopqrstuvwxyz'
for idx in range(26):
  if not alphabet[idx] in S:
    print(alphabet[idx])
    exit()
print('None')

Solution (Python):

import sys
import copy
import collections
from bisect import bisect_left
from bisect import bisect_right
from collections import defaultdict
from heapq import heappop, heappush
import math
import itertools
 




 
def inputInt(): return int(input())
def inputMap(): return map(int, input().split())
def inputList(): return list(map(int, input().split()))
 
def main():
    S = list(input())
    
    tmp = [chr(i) for i in range(97, 97+26)]
    
    for i in tmp:
        if i in S:
            continue
        else:
            print(i)
            sys.exit()
            
    print("None")
    
    
if __name__ == "__main__":
	main()

Solution (Python):
import string
li = string.ascii_lowercase
s = sorted(list(input()))
for i in range(26):
    if not li[i] in s:
        print(li[i])
        exit()
print("None")

Solution (Python):
s = input()
packet = 'abcdefghijklmnopqrstuvwxyz'
checked = [0]*26
ans = []
for i in range(len(s)):
    checked[packet.index(s[i])] = 1
for i in range(26):
    if checked[i] != 1:
        ans.append(packet[i])
ans.sort()
if sum(checked) != 26:
    print(ans[0])
else:
    print('None')

Solution (Python):
A2Z = set(map(chr, range(ord('a'), ord('z')+1)))
s = set(input())
if A2Z == s:
  print('None')
else:
  print(sorted(A2Z - s)[0])

Solution (Python):
S = input()
ans = None
for letter in "abcdefghijklmnopqrstuvwxyz":
    if letter not in S:
        ans = letter
        break
print(ans)

Solution (Python):
l=set(i for i in "abcdefghijklmnopqrstuvwxyz")
n=set(j for j in input())
b=sorted(l-n)
print("None" if b==[] else b[0])

Solution (Python):
S = input()

word_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']

for i in word_list:
    if i not in set(S):
        print(i)
        exit()

print('None')

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

Solution (Python):
s1 = sorted(input())
s2 = "abcdefghijklmnopqrstuvwxyz"

for s in s2:
  if s in s1:
    pass
  else:
    print(s)
    break
else:
  print("None")

Solution (Python):
alf = ["a","b","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(str(input()))
flag = 0
for i in alf:
    if i not in s:
        print(i)
        flag = 1
        break
if flag == 0:
    print("None")

Solution (Python):
s=set(input())
alphabet="abcdefghijklmnopqrstuvwxyz"
alp=set(alphabet)
print(min(alp - s) if len(alp-s)!=0 else "None")

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

tmp = S[0]
if tmp != 'a':
    print('a')
    exit()

for i in S:
    if ord(i) == (ord(tmp) + 1) or ord(i) == ord(tmp):
        tmp = i
    else:
        print(chr(ord(i)-1))
        exit()

if tmp == 'z':
    print("None")
else:
    print(chr(ord(i)+1))

Solution (Python):

from collections import Counter
import string

s = input()
c = Counter(s)

for x in string.ascii_lowercase:
    if c[x] == 0:
        print(x)
        break
else:
    print('None')

Solution (Python):
s = list(input())
alpha = 'abcdefghijklmnopqrstuvwxyz'
alpha_list = list(alpha)
check = [0] * 26
for i in range(len(s)):
  if check[alpha_list.index(s[i])] == 0 :
    check[alpha_list.index(s[i])] = 1
if 0 in check :
  ans = alpha_list[check.index(0)]
  print(ans)
else:
  print('None')

Solution (Python):
S = set(input())
Alph={chr(i) for i in range(97, 97+26)}
B = Alph - S
if B==set():
  print('None')
else:
  print(sorted(B)[0])

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

Solution (Python):
S = list(input())
s = set(S)
S = list(s)
S.sort()
if len(S) == 26:
    print (None)
else:
    tmp = 0
    for i in 'abcdefghijklmnopqrstuvwxyz':
        if tmp >= len(S):
            print (i)
            break
        if i == S[tmp]:
            tmp += 1
        else:
            print (i)
            break

Solution (Python):
s = input()
alpha = 'abcdefghijklmnopqrstuvwxyz'
for i in range(len(alpha)):
  if alpha[i] not in s:
    print(alpha[i])
    exit()
print('None')

Solution (Python):
from collections import defaultdict
S = input()
alphabet = list("abcdefghijklmnopqrstuvwxyz")
d = defaultdict(int)

for s in S:
     d[s] += 1
for s in alphabet:
     if d[s] == 0:
          ans = s
          break
else:
     ans = "None"
print(ans)

Solution (Python):
s = input()
letters = "abcdefghijklmnopqrstuvwxyz"
hash = {}

for chara in s:
  hash[chara] = 1
  if(len(hash) == 26):
    print("None")
    exit()

for c in letters:
  if c not in hash:
    print(c)
    exit()

Solution (Python):
a = list(input())
b = list("abcdefghijklmnopqrstuvwxyz")
for i in range(len(b)):
    c = True
    for j in range(len(a)):
        if b[i] == a[j]:
            c = False
    if c:
        print(b[i])
        exit()
print("None")

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

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

Solution (Python):
s = input()
alphabet = [0 for i in range(26)]
for i in s:
    alphabet[ord(i)-97] += 1
for i in range(len(alphabet)):
    if alphabet[i] == 0:
        print(chr(i+97))
        break
    elif i == len(alphabet) - 1:
        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):
s=set(input())
alp={"a","b","c","d","e","f","g",
     "h","i","j","k","l","m","n",
     "o","p","q","r","s","t","u",
     "v","w","x","y","z"}
if len(s) ==26:
  print("None")
else:
  print(sorted(alp-s)[0])

Solution (Python):
import string

def B():
    s = set(input())
    for c in string.ascii_lowercase:
        if c not in s:
            print(c)
            break
    else:
        print("None")

B()

Solution (Python):
import re
a = input()
a = [a[i] for i in range(len(a))]
b = "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(b.split())
a.sort()
b.sort()
for j in range(len(b)):
    c = True
    for i in range(len(a)):
        if a[i] == b[j]:
            c = not c
            break
    if c:
        print(b[j])
        exit()
print("None")

Solution (Python):
alpha = "abcdefghijklmnopqrstuvwxyz"

s = input()

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

print("None")

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

s_set = set(s)
if len(s_set) == 26:
    print('None')
else:
    for a in alpha:
        if a not in s_set:
            print(a)
            break

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

Solution (Python):
s = set(input())
s1 = set("abcdefghijklmnopqrstuvwxyz")
ans = sorted(list(s1 - s))
if ans:
    print(ans[0])
else:
    print("None")

Solution (Python):
s=set(list(str(input())))
l=[chr(i) for i in range(97, 97+26)]
for i in l:
    if i not in s:
        print(i)
        exit()
print("None")

Solution (Python):

S = input()
ss = set()
for i in range(len(S)):
    ss.add(S[i])

alpha_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']
ans = ''
for k in range(len(alpha_list)):
    if alpha_list[k] not in ss:
        ans = alpha_list[k]
        break
if len(ss) == 26:
    print('None')
else:
    print(ans)

Solution (Python):



alpha = 'abcdefghijklmnopqrstuvwxyz'
s = list(input())
for i in range(26):
    if alpha[i] not in s:
        print(alpha[i])
        quit()
print('None')

Solution (Python):
s = list(input())
alphabets = list('abcdefghijklmnopqrstuvwxyz')
for i in range(len(s)):
  if s[i] in alphabets:
    alphabets.pop(alphabets.index(s[i]))
if len(alphabets) > 0:
  print(alphabets[0])
else:
  print("None")

Solution (Python):



def read_h(typ=int):
    return list(map(typ, input().split()))


def read_v(n, typ=int):
    return [typ(input()) for _ in range(n)]


def main():
    S = input()

    for i in range(26):
        c = chr(ord('a') + i)
        if c not in S:
            print(c)
            return

    print(None)


if __name__ == '__main__':
    main()

Solution (Python):



def read_h(typ=int):
    return list(map(typ, input().split()))


def read_v(n, typ=int):
    return [typ(input()) for _ in range(n)]


def main():
    S, = read_h(str)
    flag = [False] * 26
    for c in S:
        i = ord(c) - ord('a')
        if not flag[i]:
            flag[i] = True

    ans = None
    for i, f in enumerate(flag):
        if not f:
            print(chr(i + ord('a')))
            return

    print(str(ans))


if __name__ == '__main__':
    main()

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

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

Solution (Python):
s=input()
s=set(s)
l = list(s)
l.sort()
al=['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']
for i in range(len(l)):
    if(l[i]!=al[i]):
        print(al[i])
        break
lenl=len(l)
lenl1=lenl-1
if((lenl<=25)&(l[lenl1]==al[lenl1])):
    print(al[len(l)])
if (l==al):
    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()

S = list(set(S))
S.sort()

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

for s in S:
    T[ord(s)-97] = 1

for n in range(26):
    if T[n] == 0:
        print(chr(n+97))
        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):
alphabet_set={"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=set(s)
ans_set=alphabet_set-s_set
ans_l=list(ans_set)
ans_l.sort()

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

Solution (Python):

S = input()
dic = {}

dic[" "] = 1

for i in S:
    dic[i] = 1

cha = "abcdefghijklmnopqrstuvwxyz "

for i in cha:

    if i not in dic:
        print(i)
        break

    if i == " ":
        print("None")
        break

Solution (Python):
S = input()
alphabet = "abcdefghijklmnopqrstuvwxyz"
chk_list = []
for a in alphabet:
    chk_list.append(a)

for s in S:
    if s in chk_list:
        chk_list.remove(s)

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

Solution (Python):
a = input()
b = sorted(a)
c = "abcdefghijklmnopqrstuvwxyz"

for s in c:
  if s in b:
    pass
  else:
    print(s)
    break
else:
  print("None")

Solution (Python):
S = input()
A = [chr(ord('a') + i) for i in range(26)]
c = 0

for i in range(26):
  if A[i] in S:
    continue
  else:
    print(A[i])
    c = 1
    break
if c == 0:
  print("None")

Solution (Python):
s = input().split()
s = list(s[0])
s.sort()
alf = [chr(i) for i in range(97, 97+26)]
Flag = 0
s_not_duplicate = []
s_not_duplicate.append(s[0])
for i in range(len(s)):
    if s_not_duplicate[-1] != s[i]:
        s_not_duplicate.append(s[i])

for i in range(len(alf)):
    if i > len(s_not_duplicate) - 1:
        print(alf[i])
        Flag = 1
        break
    
    if s_not_duplicate[i] != alf[i]:
        Flag = 1
        print(alf[i])
        break
if Flag == 0:
    print("None")

Solution (Python):
alpha = [chr(ord('a') + i) for i in range(26)]

s = input()
lst = list(s)
lst.sort()

for w in alpha:
    if w not in lst:
        print(w)
        exit()
print('None')

Solution (Python):
s=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"]
d=list(set(s))
d.sort()
ans="None"
for i in range(min(len(a),len(d))):
    if d[i]!=a[i]:
        ans=a[i]
        break
    u=i
if len(d)<len(a) and ans=="None":
    ans=a[u+1]
print(ans)

Solution (Python):



def num2alpha(num):
    if num <= 26:
        return chr(64 + num)
    elif num % 26 == 0:
        return num2alpha(num // 26 - 1) + chr(90)
    else:
        return num2alpha(num // 26) + chr(64 + num % 26)

s = list(input().upper())
for i in range(1, 27):
    if num2alpha(i) in s:
        continue
    else:
        print(num2alpha(i).lower())
        break
else:
    print("None")

Solution (Python):
s = set(list(map(str, input())))
alph = [chr(i) for i in range(97, 97+26)]
for c in alph:
    if c not in s:
        print(c)
        exit()
print("None")

Solution (Python):
S=input()
T=[]
result='None'
for i in range(len(S)):
  T.append(S[i])
T=list(set(T))
T.sort()
A='abcdefghijklmnopqrstuvwxyz'
for j in range(len(T)):
  if T[j]!=A[j]:
    result=A[j]
    break
  if j == (len(T)-1) and len(T) != len(A):
    result=A[j+1]
print(result)

Solution (Python):
s=input()
for i in "abcdefghijklmopqrstuvwxyz":
  if i in s:continue
  print(i)
  break
else:
  print("None")

Solution (Python):
import string
s = input()
find = False
for c in string.ascii_lowercase:
  if c not in s:
    print(c)
    find = True
    break
if not find:
  print('None')

Solution (Python):
x=input()
for i in range(26):
    num=x.count(chr(i+97))
    if num==0:
        print(chr(i+97))
        num+=1
        break
    num=0
if num==0:
    print("None")

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

s_set.sort()

chk = list("abcdefghijklmnopqrstuvwxyz")

i = 0

while 1:
    if s_set[i] != chk[i]:
        print(chk[i])
        break
    i += 1
    
    if i >= (len(s_set)):
        print(chk[i])
        break
    if i >= 25:
        print("None")
        break

Solution (Python):
def main():
    L = [0] * 26
    for s in input():
        L[ord(s) - 97] = 1
    for i, j in enumerate(L):
        if j == 0:
            print(chr(97 + i))
            return
    print('None')


main()

Solution (Python):
nl = lambda: list(map(int, input().split()))
sl = lambda: input().split()
n = lambda: int(input())
s = lambda: input()

S = s()

left = set(list('abcdefghijklmnopqrstuvwxyz'))
for c in S:
    if c in left:
        left.remove(c)

if len(left) > 0:
    print(sorted(list(left))[0])
else:
    print('None')

Solution (Python):
S = set(input())
diff = set('abcdefghijklmnopqrstuvwxyz') - S
if diff:
    print(min(diff))
else:
    print('None')

Solution (Python):
check = "abcdefghijklmnopqrstuvwxyz"
check_list = list(check)

s = list(input())
s = list(dict.fromkeys(s))
s.sort(reverse=False)

for search in check_list :
    if search not in s :
        print(search)
        exit()
        
print("None")

Solution (Python):
s=input()
ans=False

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

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

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

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

Solution (Python):
s=input()

al=list("abcdefghijklmnopqrstuvwxyz")


ans=False

for i in al:
    if not i in s:
        print(i)
        ans=True
        break

if not ans:
    print(None)

Solution (Python):
def abc():
    import string
    nf = set(string.ascii_lowercase) - set(input().rstrip())
    if len(nf):
        print(sorted(nf)[0])
    else:
        print('None')


abc()

Solution (Python):
S=input()
for i in range(26):
    s=chr(ord("a")+i)
    if s in S:
        continue
    print(s)
    quit()
print("None")

Solution (Python):
s = input()
ok = False
al = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']
for i in al:
    if i not in s:
        print(i)
        ok = True
        break
if not ok:
    print('None')

Solution (Python):
from sys import stdin
S = (stdin.readline().rstrip())
if len(set(list(S))) == 26:
    print("None")
else:
    s = set(list("abcdefghijklmnopqrstuvwxyz")) - (set(list(S)))
    print(sorted(s)[0])

Solution (Python):
s = input()
temp = 'abcdefghijklmnopqrstuvwxyz'
for i in range(26):
    if s.find(temp[i]) == -1:
        print(temp[i])
        exit()
print('None')

Solution (Python):
import bisect
import os
from collections import Counter, deque
from fractions import gcd
from functools import lru_cache
from functools import reduce
import functools
import heapq
import itertools
import math
import numpy as np
import re
import sys
import string

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

sys.setrecursionlimit(2147483647)
INF = float("inf")




S = sys.stdin.readline().rstrip()
for c in string.ascii_lowercase:
    if c not in S:
        print(c)
        exit()
print('None')

Solution (Python):

from collections import Counter

def main():
    data = input()
    for i in range(26):
        now_str = chr(i + 97)
        if now_str not in data:
            print(now_str)
            break
    else:
        print('None')



if __name__ == '__main__':
    main()

Solution (Python):
import string
string.ascii_lowercase
a = list(string.ascii_lowercase)
s = input()
s = [i for i in s]
s.sort()
for c in a:
    if s.count(c) == 0:
        print(c)
        exit()
print('None')

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

Solution (Python):
s = list(str(input()))
e = list('abcdefghijklmnopqrstuvwxyz')
sSet = set(s)
for i in sSet :
        e.remove(i)
if e == [] :
        print('None')
else :
        print(min(e))

Solution (Python):
S = sorted(set(input()))
s = [chr(i) for i in range(97,97+26)]
for i in s:
    if i not in S:
        print(i)
        break
    elif i == 'z':
        print('None')

Solution (Python):
s=input()
for i in range(26):
  if chr(97+i) not in s:
    print(chr(97+i))
    break
  if i==25 and "z" in s:
    print("None")

Solution (Python):
alpha = [chr(ord('a') + i) for i in range(26)]
s = [str(i) for i in input()]

ss = set(alpha) - set(s)
ans = list(ss)
ans = sorted(ans)
if ans == []:
    print("None")
else:
    print(ans[0])

Solution (Python):
alphabets = set(chr(ord('a')+i) for i in range(26))
alphabets -= set(input())

rest = sorted(alphabets)
answer = rest[0] if rest else 'None'

print(answer)

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"]
ans = "None"
for a in A:
    if a not in S:
        ans = a
        break
print(ans)

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 = set(input())
word = set('abcdefghijklmnopqrstuvwxyz')
word = word - S
word = sorted(word)

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

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

Solution (Python):

import sys


def solve(S: str):
    ret = None
    for i in range(26):
        c = chr(ord('a') + i)
        if not c in S:
            ret = c
            break
    print(ret)
    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):

word = list(input())
word.sort()


ans = []
for i in [chr(i) for i in range(97, 97+26)]:
  n = word.count(i)
  if n == 0:
    ans.append(i)
    break
else:
    ans.append('None')
    
    
print(ans[0])

Solution (Python):
s = input()
S = list(set(s))
list.sort(S)
strings = "abcdefghijklmnopqrstuvwxyz"
switch = 0
for i in S:
    if i != strings[S.index(i)]:
        print(strings[S.index(i)])
        switch = 1
        break
    else:
        continue
if switch == 0:
    if len(strings) == len(S):
        print("None")
    else:
        print("z")

Solution (Python):
import string

result = "None"
str = list(set(input()))
for s in string.ascii_lowercase:
  if not s in str:
    result = s
    break
print(result)

Solution (Python):
S= input()

abs = 'abcdefghijklmnopqrstuvwxyz'

for ab in abs:
  if not ab in S:
    print(ab)
    exit()
else: print('None')

Solution (Python):
import sys

s = list(set(list(input())))
s.sort()

for i in range(len(s)):
    if s[i] != chr(ord("a") + i):
        print(chr(ord("a") + i))
        sys.exit()
if len(s) < 26:
  	print(chr(ord("a") + len(s)))
else:
	print("None")

Solution (Python):
import sys

s = list(input())
set_s = set(s)
new_s = list(set_s)
new_s.sort()
for i in range(26):
    if ord(new_s[i]) != 97+i:
        print(chr(97+i))
        sys.exit()
    if len(new_s) == i+1:
        if i == 25:
            break
        print(chr(98+i))
        sys.exit()
print('None')

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

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

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

Solution (Python):
s = sorted(list(set(input()))) + ["A"] *26
t = "abcdefghijklmnopqrstuvwxyz"

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

Solution (Python):


s = input()

alph = 'abcdefghijklmnopqrstuvwxyz'
ar = [0 for i in range(26)]

for i in range(len(s)):
    ar[alph.find(s[i])] += 1

for i in range(len(s)):
    if 0 not in ar:
        print('None')
        break
    if ar[i] == 0:
        print(alph[i])
        break

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

Solution (Python):











import sys
input=sys.stdin.readline
from math import floor,ceil,sqrt,factorial
from heapq import heappop, heappush, heappushpop
from collections import Counter,defaultdict
inf=float('inf')
mod = 10**9+7
def INT_(n): return int(n)-1
def MI(): return map(int,input().split())
def MF(): return map(float, input().split())
def MI_(): return map(INT_,input().split())
def LI(): return list(MI())
def LI_(): return [int(x) - 1 for x in input().split()]
def LF(): return list(MF())
def LIN(n:int): return [I() for _ in range(n)]
def LLIN(n: int): return [LI() for _ in range(n)]
def LLIN_(n: int): return [LI_() for _ in range(n)]
def LLI(): return [list(map(int, l.split() )) for l in input()]
def I(): return int(input())
def F(): return float(input())
def ST(): return input().replace('\n', '')
def main():
    S = ST()
    d = defaultdict(int)
    for s in S:
        d[s] += 1
    for i in range(26):
        if d[chr(i + ord("a"))] == 0:
            print(chr(i + ord("a")))
            exit()
    print("None")

            
if __name__ == '__main__':
    main()

Solution (Python):
def judge(lst):
	for i in range(0, 26):
		if lst[i] == 0: return str(chr(i+97))
	return('None')

S = input()
countlist = []
for i in range(0, 26):
	countlist.append(0)
for i in range(0, len(S)):
	countlist[ord(S[i])-97] += 1
print(judge(countlist))

Solution (Python):
s = input()
char = {i for i in s}
if len(char) == 26:
    print('None')
else:
    for i in 'abcdefghijklmnopqrstuvwxyz':
        if i not in char:
            print(i)
            break

Solution (Python):
s = input()

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

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

Solution (Python):
S = list(input())
a_to_z = "abcdefghijklmnopqrstuvwxyz"
S.sort()
ans = "None"
for string in a_to_z:
    if string not in S:
        ans = string
        break
print(ans)

Solution (Python):
s = input()
ans = []
for i in range(ord("a"),ord("z")+1):
    if chr(i) not in s:
        ans.append(chr(i))

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

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

Solution (Python):
s = input()

ans = [ chr(i) for i in range(ord("a"),ord("z")+1) if chr(i) not in s]

ans.sort()

if len(ans) == 0:
    print("None")
else:
    print(ans[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 = list(input())
S = list(set(S))
count = 0

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 a in Alpha:
    for s in S:
        if s != a:
            count += 1
        else:
            break
        
    if  count == len(S):
        print(a)
        exit()
    else:
        count = 0

print('None')

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

Solution (Python):
s = input()
alpha = "abcdefghijklmnopqrstuvwxyz"
out = ""

for a in alpha :
	if a not in s :
		out = a
		break
print(out if out != "" else "None")

Solution (Python):
S=list(input())
S= list(set(S))
J=[]
S.sort()
for i in range(97,123):
    A=chr(i)
    J.append(A)
for i in S:
    J.remove(i)
if len(J)==0:
    print('None')
else:
    print(J[0])

Solution (Python):

alphabet = [chr(ord('a')+i) for i in range(26)]
S=list(set(input()))
S.sort()

for i in alphabet:
    if i not in S:
        print(i)
        exit()
print("None")

Solution (Python):
import string

S=set(input())
letters_set=set(string.ascii_lowercase)
a=letters_set-S

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

Solution (Python):
S = input()

word_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']

for i in word_list:
    if i not in S:
        print(i)
        exit()

print('None')

Solution (Python):

import sys

ALPHABETS = "abcdefghijklmnopqrstuvwxyz"


def solve(S: str):
    for alphabet in ALPHABETS:
        if alphabet not in S:
            print(alphabet)
            return
    print("None")
    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()
ans='a'

while ans in S and ord(ans)!=ord('z')+1:
    ans=chr(ord(ans)+1)

print(ans if ord(ans)!=ord('z')+1 else 'None')

Solution (Python):
S = [ord(c) for c in list(input())]

def main():
    ans = None
    for n in range(ord('a'), ord('z') + 1):
        if S.count(n) == 0:
            ans = chr(n)
            break
    print(ans)

if __name__ == '__main__':
    main()

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

Solution (Python):
l=set(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"}
ans=sorted(list(x-l))
print("None" if ans==[] else ans[0])