#include <bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c,d;
	cin>>a>>b>>c>>d;
	int t1,t2;
	t1=a/d;
	if (a%d) t1++;
	t2=c/b;
	if (c%b) t2++;
	if (t1>=t2) cout<<"Yes"<<endl;
	else cout<<"No"<<endl;
	return 0;
}