import java.util.Scanner;
public class Main{

	public static void main(String[] args) {
		Scanner stdIn=new Scanner(System.in);
		int A=stdIn.nextInt();
		int B=stdIn.nextInt();
		int C=stdIn.nextInt();
		int D=stdIn.nextInt();
		
		while(A>0&&C>0) {
			C=C-B;
			if(C<=0)break;
			A=A-D;
		}
		if(A<=0)
			System.out.println("No");
		else
			System.out.println("Yes");

	}

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz