Deleting digits

warning: unused imports: `max`, `min`
 --> input/code.rs:1:16
  |
1 | use std::cmp::{max, min};
  |                ^^^  ^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: unused imports: `HashMap`, `HashSet`
 --> input/code.rs:2:24
  |
2 | use std::collections::{HashMap, HashSet};
  |                        ^^^^^^^  ^^^^^^^

warning: 2 warnings emitted

use std::cmp::{max, min};
use std::collections::{HashMap, HashSet};
use std::io::{self, Read};

macro_rules! input {
    ($it: expr) => {
        $it.next().unwrap().parse().unwrap()
    };
    ($it: expr, $T: ty) => {
        $it.next().unwrap().parse::<$T>().unwrap()
    };
}
/*
mod classes;
mod homework;

fn main() {
    // println!("{}", "-".repeat(20));
    classes::c09::task1();
    // homework::hw3::task1();
    // println!("{}", "-".repeat(20));
}
// */

fn main() {
    let mut buf = String::new();
    io::stdin().read_to_string(&mut buf).unwrap();

    let mut it = buf.split_whitespace();

    let mut n: u32 = input!(it);

    let mut steps = 0;
    while n > 0 {
        let max_digit = n.to_string()
            .chars()
            .map(|c| c.to_digit(10).unwrap())
            .max()
            .unwrap();

        n -= max_digit;

        steps += 1;
    }
    println!("{}", steps);
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED