#include <stdio.h>

int		main()
{
	int		A, B, C,D;
	int		t, a;

	scanf("%d %d %d %d\n", &A, &B, &C,&D);
	t = A / D;
	if (A % D)
		t++;
	a = C / B;
	if (C % B)
		a++;
	if (t >= a)
		printf("Yes\n");
	else
		printf("No\n");
	return (0);
}
