#include <stdio.h>

int	main(void)
{
	int taka_hp, taka_of, aoki_hp, aoki_of;
	scanf("%d %d %d %d", &taka_hp, &taka_of, &aoki_hp, &aoki_of);

	while (taka_hp >= 0 && aoki_hp >= 0)
	{
		taka_hp = taka_hp - aoki_of;
		aoki_hp = aoki_hp - taka_of;
	}
	if (taka_hp <= 0)
		printf("No\n");
	else
		printf("Yes\n");

	return (0);
}