#include<bits/stdc++.h>
using namespace std;
#define ll long long
int a,b,c,d; 
int main()
{
   cin>>a>>b>>c>>d;
   while(1)
   {
   	   c-=b;
   	  
   	   if(a<=0) {
   	   	cout<<"No"<<endl;return 0;
		  }
      a-=d;
		if(c<=0){
   	   	cout<<"Yes"<<endl;return 0;
		  }
   }


return 0;
}
