public class No_166 {

	public static void main(String[] args) {
		java.util.Scanner sc = new java.util.Scanner(System.in);
		long l = sc.nextLong() * sc.nextLong();
		int n = sc.nextInt();
		int k = sc.nextInt();
		String ans = "";

		if (k == l % n || l == k) {
			ans = "YES";
		} else {
			ans = "NO";
		}

		System.out.println(ans);
		sc.close();

	}

}