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::io::stdin;
fn main() {
    let mut st = String::new();
    stdin().read_line(&mut st).unwrap();
    let n:String = st.trim().parse().unwrap();
    let x:Vec<char> = n.chars().collect();
    let y = x.len();
    if x[1..].iter().all(|&x| x as i32 -48 == 9) {
        let r:i32 = x[1..].iter().map(|&x| x as i32 -48).sum();
        println!("{:?}",r+(x[0] as i32 - 48));
    } else {
        println!("{:?}", 9*(y-1)+(x[0] as usize - 48)-1)
    }
}