#include <stdio.h>

int main(void)
{
	int life1, atk1;
	int life2, atk2;
	int i;

	scanf("%d%d%d%d", &life1, &atk1, &life2, &atk2);

	for (i = 0; life1 > 0 && life2 > 0; i++)
	{
		life2 -= atk1;
		life1 -= atk2;
	}

	if (life2 <= 0)
	{
		printf("Yes");
	}
	else
	{
		printf("No");
	}

	return 0;
}