use std::error::Error;
use std::fs::File;
use std::io::{self, BufRead};
use std::vec::Vec;

fn main() -> Result<(), Box<dyn Error>> {
    let file = File::open("inputs/day13.txt")?;
    let mut lines = io::BufReader::new(file).lines().map(|l| l.unwrap());

    let buses: Vec<Option<u64>> = lines
        .nth(1)
        .unwrap()
        .split(',')
        .map(|b| b.parse().ok())
        .collect();

    let mut step = buses[0].unwrap();
    let mut t: u64 = 0;
    for i in 1..buses.len() {
        if let Some(bus) = buses[i] {
            loop {
                t = t + step;
                if (t + i as u64) % bus == 0 {
                    step = step * bus;
                    break;
                }
            }
        }
    }

    println!("{}", t);

    Ok(())
}