package test;

import java.util.Scanner;


public class atc {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		long h=sc.nextInt();
		long w=sc.nextInt();
		long n=sc.nextInt();
		long k=sc.nextInt();
		long ans=(h+w-1)%n;
		if(ans==0)ans=n;
		if(ans==k)	System.out.println("YES");
		else System.out.println("NO");
	}

}