import java.util.*;

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