#include <stdio.h>
#include <stdlib.h>
int main()
{
	int A,B,C,D;
	scanf("%d %d %d %d",&A,&B,&C,&D);
	while(1)
	{
		C = C - B;
		if(C<=0)
		{
			printf("Yes");
			break;
		}
		A = A - D;
	    if(A<=0)
	    {
			printf("No");
			break;
		}		
	}

	return 0;
}