#include <iostream>
#include <vector>
#include <queue>
#include <string>
#include <algorithm>
typedef long long ll;
const int MOD = 1000000007;
#define PI 3.141592653589
using namespace std;

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