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

int main() {
	int a, b, c, d, ans;
	cin >> a >> b >> c >> d;
	while (1) {
		c -= b;
		if (c <= 0) {
			ans = 0;
			break;
		}
		a -= d;
		if (a <= 0) {
			ans = 1;
			break;
		}
	}
	if (ans) {
		cout << "No" << endl;
	}
	else {
		cout << "Yes" << endl;
	}
}