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: Wrong Answer)

let n = read_int ()
let rec f n i j = if n < 10 then j else f (n / 10) (i + 1) @@ if n mod 10 = 9 then j else i + 1
let rec g s n i j = if n = 0 then s else g (s + if i = j then n mod 10 - 1 else if i > j then n mod 10 else 9) (n / 10) (i + 1) j
let j = f n 0 ~-1
let _ = Printf.printf "%d\n" @@ if j = -1 then n else g 0 n 0 j