import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final long H = sc.nextLong();
		final long W = sc.nextLong();
		final long N = sc.nextLong();
		final long K = sc.nextLong();
		
		final long MAX = Math.max(H, W);
		final long MIN = Math.min(H, W);
		// MAX回 ~ MAX + MIN 回 までの間に居ると負けずに死ぬように行動される?
		
		final long MAX_MOD_N = MAX % N;
		final long DIST = MAX_MOD_N < K ? ((N - 1) - MAX_MOD_N) + K : (K - 1) - MAX_MOD_N;
		
		System.out.println(DIST <= MIN ? "YES" : "NO");
	}

}