import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		new Main().solver();
	}
	void solver(){
		Scanner sc=new Scanner(System.in);
		long H=sc.nextLong();
		long W=sc.nextLong();
		long N=sc.nextLong();
		long K=sc.nextLong();
		
		if((H+W-1)%N==K%N){
			System.out.println("YES");
		}else{
			System.out.println("NO");
		}
	}
}