#include <bits/stdc++.h>
using namespace std;

int main() {
	long n,m,i,j,k,a,b,c,d,ans,cur,res;
	cin >> a >> b >> c >> d;
	if((c+b-1)/b >(a+d-1)/d){
		cout << "No" << endl;
	}else{
		cout << "Yes" << endl;
	}
	return 0;
}