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 { System.out.println("NO"); } } }