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::*;

fn main() {
    let i = stdin();
    solve(&mut i.lock(), &mut stdout());
}

fn solve(i: &mut BufRead, o: &mut Write) {
    let n_str = read_line(i);
    let n0: usize = n_str[0..1].parse().unwrap();
    let r = (n0 - 1) + 9 * (n_str.len() - 1);

    writeln!(o, "{}", r).unwrap();
}

fn read_line(i: &mut BufRead) -> String {
    let mut line = String::new();
    i.read_line(&mut line).unwrap();
    line.trim().to_string()
}