#include <stdio.h>

int main(void)
{
	int a, b, c, d, who = 0;

	scanf("%d %d %d %d", &a, &b, &c, &d);

	while (1)
	{
		++who;

		if (who % 2)
			c -= b;
		else
			a -= d;

		if (a <= 0)
		{
			puts("No");
			return 0;
		}
		else if (c <= 0)
		{
			puts("Yes");
			return 0;
		}
	}
}