#include<iostream>
using namespace std;

int main() {
	int A, B, C, D;
	cin >> A >> B >> C >> D;
	for (int i = 1; A <= 0 || C <= 0; i++)
		if (i % 2 == 1)
			C = C - B;
		else
			A = A - D;
		
	if (A <= 0)
		cout << "No";
	else
		cout << "Yes";
	

}