#![feature(iter_advance_by)]
use std::collections::HashMap;
use std::env;
struct ElfGame {
    history: HashMap<usize, usize>,
    last: usize,
    len: usize,
}
impl ElfGame {
    fn new() -> Self {
        ElfGame {
            history: HashMap::new(),
            last: 0,
            len: 0,
        }
    }
    fn push(&mut self, num: usize) {
        self.history.insert(self.last, self.len);
        self.len += 1;
        self.last = num;
    }
}
impl Iterator for ElfGame {
    type Item = usize;
    fn next(&mut self) -> Option<Self::Item> {
        let nxt = self.history.get(&self.last)
            .map_or_else(|| 0, |p| self.len - p);
        self.push(nxt);
        Some(nxt)
    }
}
fn main() {
    use std::io::BufReader;
    use std::io::BufRead;
    use std::fs::File;
    use std::path::Path;
    use std::str::FromStr;
    let mut eg = ElfGame::new();
    let args: Vec<_> = env::args().collect();
    let file = BufReader::new(File::open(<String as AsRef<Path>>::as_ref(&args[2])).unwrap());
    for strnum in file.split(b',') {
        match <usize as FromStr>::from_str(String::from_utf8(strnum.unwrap_or(vec![])).unwrap_or("".to_string()).trim()) {
            Ok(num) => {
                eg.push(num);
            }
            Err(_) => ()
        }
    }
    match eg.advance_by(<usize as FromStr>::from_str(args[1].as_ref()).unwrap() - eg.len - 1) {
        Ok(_) => println!("{}", eg.next().unwrap()),
        Err(err) => eprintln!("{:?}", err),
    }
}