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

int main() {
 int A, B, C, D;
 cin >> A >> B >> C >> D;
  
 if (C /B > A /D){
   cout << "No" << endl;
 }
 else if(C /B < A /D){
   cout << "Yes" << endl;
 }
  else if (C /B == A /D && A % D==0 && C % B!=0){
  cout << "No" << endl;
  } else {cout << "Yes" << endl;}
}

