Advent of Code 2016 Day 9 part 2

#![allow(unused_imports)]
#![allow(dead_code)]
extern crate regex;
use regex::Regex;
use std::collections::{HashMap, HashSet};
use std::io;

fn read_line() -> String {
    let mut input = String::new();
    io::stdin().read_line(&mut input).unwrap();
    input.trim_right().to_owned()
}

fn parse_usize<'a, T: Into<&'a str>>(s: T) -> usize {
    s.into().parse().unwrap()
}

fn decompress(s: &str) -> usize {
    let mut out = 0;
    let mut cur_slice = s;
    loop {
        match cur_slice.find('(') {
            Some(pos) => {
                out += pos;
                cur_slice = &cur_slice[pos..];
                match cur_slice.find(')') {
                    Some(pos) => {
                        let enc = &cur_slice[1..pos];
                        cur_slice = &cur_slice[pos+1..];
                        let xpos = enc.find('x').unwrap();
                        let cnt = parse_usize(&enc[0..xpos]);
                        let rep = parse_usize(&enc[xpos+1..]);
                        let replen = decompress(&cur_slice[0..cnt]);
                        out += rep * replen;
                        cur_slice = &cur_slice[cnt..];
                    },
                    _ => unreachable!(),
                }
            },
            _ => {
                out += cur_slice.len();
                break;
            },
        }
    }
    out
}

fn main() {
    let mut sum = 0;
    let mut input = "".to_string();
    loop {
        let line = read_line();
        if line.is_empty() { break };
        input.push_str(&line[..]);
    };
    input.replace(char::is_whitespace,"");
    let out = decompress(&input[..]);

    println!("{:?}", out);
}