fn main() {
    let mut hwnk = String::new();
    std::io::stdin().read_line(&mut hwnk).ok();
    let hwnk: Vec<usize> = hwnk.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let h = hwnk[0];
    let w = hwnk[1];
    let n = hwnk[2];
    let k = hwnk[3];

    if (h+w-2) % n + 1 == k {
        println!("YES");
    } else {
        println!("NO");
    }
}