Problem:
Score : 300 points

Problem Statement

Find the maximum possible sum of the digits (in base 10) of a positive integer not greater than N.

Constraints

1\leq N \leq 10^{16}

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the maximum possible sum of the digits (in base 10) of a positive integer not greater than N.

Sample Input 1

100

Sample Output 1

18

For example, the sum of the digits in 99 is 18, which turns out to be the maximum value.

Sample Input 2

9995

Sample Output 2

35

For example, the sum of the digits in 9989 is 35, which turns out to be the maximum value.

Sample Input 3

3141592653589793

Sample Output 3

137

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Data.Char

main = do
  n <- getLine

  print $ maximum $ map (sum . map (\c -> ord c - ord '0')) (solve [] n)

  where
    solve pre [] = [pre]
    solve pre (x:xs) = (pre ++ (chr (ord x - 1) : map (const '9') xs)) : solve (pre++[x])xs