#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

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

	cin >> A >> B >> C >> D;

	while (true)
	{
		C -= B;
		if (C <= 0)
		{
			cout << "Yes" << endl;
			break;
		}

		A -= D;
		if (A <= 0)
		{
			cout << "No" << endl;
			break;
		}
	}

	return 0;
}