import java.util.*;

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