import java.util.Scanner; public class Main { static int[] an = new int[1000000]; 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((H + W - 1) % N == K) System.out.println("YES"); else System.out.println("NO"); } }