#include<iostream>

using namespace std;

typedef long long ll;

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

	while (A > 0 && C > 0) {
		C -= B;
		if (C <= 0) {
			cout << "Yes\n";
			return 0;
		}
		A -= D;
		if (A <= 0) {
			cout << "No\n";
		}
	}
	return 0;
}