#include<stdio.h>
int main()
{
	int a, b, c, d;
	scanf("%d %d %d %d", &a, &b, &c, &d);
	for (;;)
	{
		c -= b;
		if (c <= 0)
			break;
		a -= d;
		if (a <= 0)
			break;
	}
	if (a > 0)
		printf("Yes\n");
	else
		printf("No\n");
	return 0;
}