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

  int BB, CC;
 
  if (B >= C){
    cout << "Yes" << endl;
    return 0;
  }

  BB = C / B;
  if (C % B != 0){
    BB += 1;
  }
  
  CC = A / D;
  if (A % D != 0){
    CC += 1;
  }
  
  
//  cout << BB << CC << endl; 
 
  if (BB > CC){
    cout << "No" << endl;
  } else {
    cout << "Yes" << endl;
  }
}