package test;

import java.util.Scanner;


public class atc {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int h=sc.nextInt();
		int w=sc.nextInt();
		int n=sc.nextInt();
		int k=sc.nextInt();
		int ans=(h+w-1)%n;
		if(ans==k)	System.out.println("YES");
		else System.out.println("NO");
	}

}