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 (1.15.1) (judge verdict: Wrong Answer)

use std::io::prelude::*;
use std::io::stdin;
use std::str::FromStr;

fn main() {
    let s: Vec<char> = read::<String>().chars().collect();

    let ans = if s[0] != '9' {
        s[0] as i64 - '1' as i64
    } else {
        let mut tmp = 9;
        for &c in s.iter() {
            if c != '9' {
                tmp = c as i64 - '1' as i64;
            }
        }
        tmp
    } + (s.len() as i64 - 1) * 9;

    println!("{}", ans);
}

#[allow(dead_code)]
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let token: String = stdin
        .lock()
        .bytes()
        .map(|b| b.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().unwrap()
}