#include <algorithm>
#include <bitset>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <string>
#include <vector>
#include <regex>

using namespace std;
using ll = long long int;
const ll MOD = 1e9 + 7;

int main() {
	ll A, B, C, D;
	cin >> A >> B >> C >> D;

	ll t = (A + D - 1) / D;
	ll u = (C + B - 1) / B;

	if (u > t) {
		cout << "No" << endl;
	}
	else {
		cout << "Yes" << endl;
	}
}