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

int main() {
  int A,B,C,D;
  cin>>A>>B>>C>>D;
  if (A/D > C/B){
    cout<<"Yes"<<endl;
  }
  else if (A/D ==C/B){
    if ((A%D)>(C%B)){
      cout<<"Yes"<<endl;
    }
    else{
      cout<<"No"<<endl;
    }
  }
  else {
    cout<<"No"<<endl;
  }
}