#include <iostream>
using namespace std;

int main()
{
	int a, b, c, d;
	cin >> a >> b >> c >> d;
	int x = c / b;
	if (c % b != 0)
		x++;
	int y = a / d;
	if (a % d != 0)
		y++;
	if (x <= y)
		cout << "Yes" << endl;
	else
		cout << "No" << endl;
	return 0;
}