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::cmp::*;
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 tmp = n * 9;
    let mut pittari = 0;
    let mut ans = 0;
    for i in 0..n {
        tmp -= 9;
        let x = (s[i] - '0' as u8) as usize;
        if x > 0 {
            ans = max(ans, pittari + tmp + x - 1);
        }
        pittari += x;
        ans = max(ans, pittari);
    }
    println!("{}", ans);
}