import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

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

}