#include <bits/stdc++.h>
using namespace std;
     
int main() {
    int A, B, C, D;
    cin >> A >> B >> C >> D;

  while(C>0 && A>0){
      C=C-B;
      A=A-D;
  }

  if(C<=0){
    cout << "Yes" << endl;
  }
  else{
    cout << "No" << endl;
  }
   
  return 0;
}