#include <stdlib.h>
#include <stdio.h>

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

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

	while(a > 0 && c > 0)
	{
		c = c - b;
		if(c > 0)
			a = a - d;
	}
	if(a <= 0)
		printf("No");
	else
		printf("Yes");
	return (0);
}