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 OCaml (4.02.3) (judge verdict: Accepted)

Printf.printf "%d\n" @@ Scanf.scanf "%s" @@ fun s ->
  let t = Array.init (String.length s) (fun i -> s.[i]) in
  let x = Array.fold_left (fun z c -> z + (int_of_char c - 48) mod 10) 0 t in
  (int_of_char s.[0] - 49) + (9 * (String.length s - 1)) |> max x