fn main() {
    let mut xx = String::new();
    std::io::stdin().read_line(&mut xx).ok();
    let xx: Vec<usize> = xx.split_whitespace().flat_map(str::parse).collect();

    let (p, q, r, k) = (xx[0], xx[1], xx[2], xx[3]);

    let mut seq = vec![p % 10, q % 10, r % 10];
    loop {
        let last3 = &seq[seq.len() - 3..];
        if seq.windows(3).position(|x| x == last3).unwrap() < seq.len() - 3 {
            seq.resize(seq.len() - 3, 0);
            break;
        }
        seq.push((last3[0] + last3[1] + last3[2]) % 10);
    }

    println!("{}", seq[(k - 1) % seq.len()]);
}