#include <bits/stdc++.h>
using namespace std;

int main() {
	int a, b, c, d;
	cin >> a >> b >> c >> d;

	while (true) {
		c -= b;
		if (c <= 0) {
			cout << "Yes" << endl;
			break;
		}
		a -= d;
		if (a <= 0) {
			cout << "No" << endl;
			break;
		}

	}

}
