#include <iostream>
#include <iomanip>
#include <algorithm>
#include <utility>
#include <cmath>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <deque>

using namespace std;

using ll = long long;
using P = pair<int, int>;

#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define mkp(a, b) make_pair(a, b)
const int inf = 1e+9;

const ll mod = 1000000007;

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

	if ((a + d - 1) / d >=  (c + b - 1) / b) {
		cout << "Yes" << endl;
	} else {
		cout << "No" << endl;

	}
	return 0;
}
