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

int main() {
  int A,B,C,D;
  cin>>A>>B>>C>>D;
  int N = (A%D)+(A/D);
  int M = (C%B)+(C/B);
  int t = A-N*D;
  int a = C-N*B;
  if (N>=M){
    cout<<"Yes"<<endl;
  }
  
  else {
    cout<<"No"<<endl;
  }
    

}