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