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: import sys
  
  
  ## io ##
  def IS():
      return sys.stdin.readline().rstrip()
  
  
  def II():
      return int(IS())
  
  
  def MII():
      return list(map(int, IS().split()))
  
  
  def MIIZ():
      return list(map(lambda x: x - 1, MII()))
  
  
  ## dp ##
  def DD2(d1, d2, init=0):
      return [[init] * d2 for _ in range(d1)]
  
  
  def DD3(d1, d2, d3, init=0):
      return [DD2(d2, d3, init) for _ in range(d1)]
  
  
  ## math ##
  def to_bin(x: int) -> str:
      return format(x, "b")  # rev => int(res, 2)
  
  
  def to_oct(x: int) -> str:
      return format(x, "o")  # rev => int(res, 8)
  
  
  def to_hex(x: int) -> str:
      return format(x, "x")  # rev => int(res, 16)
  
  
  MOD = 10**9 + 7
  
  
  def divc(x, y) -> int:
      return -(-x // y)
  
  
  def divf(x, y) -> int:
      return x // y
  
  
  def gcd(x, y):
      while y:
          x, y = y, x % y
      return x
  
  
  def lcm(x, y):
      return x * y // gcd(x, y)
  
  
  def enumerate_divs(n):
      """Return a tuple list of divisor of n"""
      return [(i, n // i) for i in range(1, int(n**0.5) + 1) if n % i == 0]
  
  
  def get_primes(MAX_NUM=10**3):
      """Return a list of prime numbers n or less"""
      is_prime = [True] * (MAX_NUM + 1)
      is_prime[0] = is_prime[1] = False
      for i in range(2, int(MAX_NUM**0.5) + 1):
          if not is_prime[i]:
              continue
          for j in range(i * 2, MAX_NUM + 1, i):
              is_prime[j] = False
      return [i for i in range(MAX_NUM + 1) if is_prime[i]]
  
  
  ## libs ##
  from itertools import accumulate as acc
  from collections import deque, Counter
  from heapq import heapify, heappop, heappush
  from bisect import bisect_left
  
  # ======================================================#
  
  
  def main():
      n = II()
      s = str(n)
      d = len(s)
      maxv = 0
      for i in range(d):
          l = sum(int(si) for si in s[:i])
          l += int(s[i]) - 1
          l += 9 * (d - i - 1)
          maxv = max(maxv, l)
      print(maxv)
  
  
  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"}]