fn main() {
    let mut nm = String::new();
    std::io::stdin().read_line(&mut nm).ok();
    let nm: Vec<usize> = nm.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let m = nm[1];
    let mut xy = String::new();
    std::io::stdin().read_line(&mut xy).ok();
    let xy: Vec<usize> = xy.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let x = xy[0];
    let y = xy[1];

    let a = x % (2*m);
    let a = if a > m { 2 * m - a + 1 } else if a > 0 { a } else { 1 };
    let b = y % (2*m);
    let b = if b > m { 2 * m - b + 1 } else if b > 0 { b } else { 1 };
    println!("{}", if a == b { "YES" } else { "NO" });
}