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