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 whiteread::parse_line;

fn main() {
    let x: usize = parse_line().unwrap();
    let xs = x.to_string();
    let left: usize = xs[0..1].parse().unwrap();
    let ans = left + 9 * (xs.len() - 1);
    let mut maxv: Vec<usize> = vec![left];
    for _ in 0..xs.len() - 1 {
        maxv.push(9);
    }
    let max: usize = maxv.iter().fold(0, |x, y| x * 10 + y);

    if max <= x {
        println!("{}", ans);
    } else {
        println!("{}", ans - 1);
    }
}