import java.util.*;

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