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 Rust (1.42.0) (judge verdict: Accepted)

use std::io::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let s: Vec<u8> = itr.next().unwrap().bytes().collect();
    let n = s.len();
    let mut dp = vec![vec![vec![false; 200]; 2]; n + 1];
    dp[0][0][0] = true;
    for i in 0..n {
        let x = (s[i] - '0' as u8) as usize;
        for j in 0..=9 {
            for k in 0..160 {
                if j == x {
                    dp[i + 1][0][j + k] |= dp[i][0][k];
                } else if j < x {
                    dp[i + 1][1][j + k] |= dp[i][0][k];
                }
                dp[i + 1][1][j + k] |= dp[i][1][k];
            }
        }
    }

    let mut ans = 0;
    for i in 0..160 {
        if dp[n][0][i] || dp[n][1][i] {
            ans = i;
        }
    }
    println!("{}", ans);
}