#include<stdio.h>

int main(void)
{
	int a, b, c, d;
	scanf("%d %d %d %d", &a, &b, &c, &d);
	while (1)
	{
		c = c - b;

		if (c <= 0)
		{
			printf("Yes");
			return 0;
		}


		a = a - d;

		if (a <= 0)
		{
			printf("No");
			return 0;
		}

	}

	return 0;
}