import java.util.*;

public class Main {
	static Scanner sc = new Scanner(System.in);
	public static void main(String[] args) {
		long H = sc.nextLong();
		long W = sc.nextLong();
		long n = sc.nextLong();
		long k = sc.nextLong();
		System.out.println((H+W-2)%n+1==k?"YES":"NO");
	}
}