题解 | #截取字符串#

use std::io::{self, *};

fn main() {
   let stdin = io::stdin();
    let mut input = String::new();
    stdin.read_line(&mut input).unwrap();
    let mut num = String::new();
    stdin.read_line(&mut num).unwrap();
    let num = num.trim().parse::<usize>().unwrap();
    input.truncate(num);
    println!("{}",input);
}