import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long H = sc.nextLong(), W = sc.nextLong(), N = sc.nextLong(), K = sc.nextLong();
        sc.close();
        if (((H - 1) + (W - 1)) % N + 1 == K) System.out.print("YES");
        else System.out.print("NO");
    }
}