import java.util.Scanner;

public class Test {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong()+sc.nextLong()-1, a = sc.nextLong(), b = sc.nextLong();
		if((n-b)%a == 0){
			System.out.println("YES");
		} else {
			System.out.println("NO");
		}
	}
}