output_description: Print the maximum possible sum of the digits (in base 10) of a positive
  integer not greater than N.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: # -*- coding: utf-8 -*-
  import sys
  import math
  import os
  import itertools
  import string
  import heapq
  import _collections
  from collections import Counter
  from collections import defaultdict
  from functools import lru_cache
  import bisect
  import re
  import queue
  
  
  class Scanner:
      @staticmethod
      def int():
          return int(sys.stdin.readline().rstrip())
  
      @staticmethod
      def string():
          return sys.stdin.readline().rstrip()
  
      @staticmethod
      def map_int():
          return [int(x) for x in Scanner.string().split()]
  
      @staticmethod
      def string_list(n):
          return [input() for i in range(n)]
  
      @staticmethod
      def int_list_list(n):
          return [Scanner.map_int() for i in range(n)]
  
      @staticmethod
      def int_cols_list(n):
          return [int(input()) for i in range(n)]
  
  
  class Math:
      @staticmethod
      def gcd(a, b):
          if b == 0:
              return a
          return Math.gcd(b, a % b)
  
      @staticmethod
      def lcm(a, b):
          return (a * b) // Math.gcd(a, b)
  
      @staticmethod
      def roundUp(a, b):
          return -(-a // b)
  
      @staticmethod
      def toUpperMultiple(a, x):
          return Math.roundUp(a, x) * x
  
      @staticmethod
      def toLowerMultiple(a, x):
          return (a // x) * x
  
      @staticmethod
      def nearPow2(n):
          if n <= 0:
              return 0
          if n & (n - 1) == 0:
              return n
          ret = 1
          while n > 0:
              ret <<= 1
              n >>= 1
          return ret
  
      @staticmethod
      def sign(n):
          if n == 0:
              return 0
          if n < 0:
              return -1
          return 1
  
      @staticmethod
      def isPrime(n):
          if n < 2:
              return False
          if n == 2:
              return True
          if n % 2 == 0:
              return False
          d = int(n**0.5) + 1
          for i in range(3, d + 1, 2):
              if n % i == 0:
                  return False
          return True
  
  
  class PriorityQueue:
      def __init__(self, l=[]):
          self.__q = l
          heapq.heapify(self.__q)
          return
  
      def push(self, n):
          heapq.heappush(self.__q, n)
          return
  
      def pop(self):
          return heapq.heappop(self.__q)
  
  
  MOD = int(1e09) + 7
  INF = int(1e15)
  
  
  def calc(N):
      return sum(int(x) for x in str(N))
  
  
  def main():
      # sys.stdin = open("sample.txt")
      N = Scanner.int()
  
      ans = calc(N)
      ans = max(ans, calc(int(str(int(str(N)[0]) - 1) + "9" * (len(str(N)) - 1))))
      ans = max(ans, calc(N - N % 10 - 1))
      print(ans)
      return
  
  
  if __name__ == "__main__":
      main()
  
problem_description: Statement
  
  Find the maximum possible sum of the digits (in base 10) of a positive integer
  not greater than N.
samples: [{"input": "100", "output": "18\n    \n\nFor example, the sum of the digits in 99 is 18, which turns out to be the\nmaximum value.\n\n* * *"}, {"input": "9995", "output": "35\n    \n\nFor example, the sum of the digits in 9989 is 35, which turns out to be the\nmaximum value.\n\n* * *"}, {"input": "3141592653589793", "output": "137"}]