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: Accepted)

use std::{io};


fn main() {
    let mut input = String::new();
    let _ = io::stdin().read_line(&mut input).unwrap();
    let mut n = input.as_bytes().iter().take_while(|x| 0x30 <= **x && **x <= 0x39).map(|x| (x - 0x30) as i32).collect::<Vec<i32>>();
    let mut s = 0;
    for i in (1..n.len()).rev() {
        s += 9;
        if n[i] < 9 {
            n[i-1] -= 1;
        }
    }
    s += n[0];
    println!("{}", s);
}