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

int main() {
  int A,B,C,D;
  cin >> A >> B >> C >> D;
  
  int n_takahashi = 0;
  while(C > 0){
    C -= B;
    n_takahashi++;
  }
  
  int n_aoki = 0;
  while(A > 0){
    A -= D;
    n_aoki++;
  }
  
  if (n_takahashi <= n_aoki) cout << "Yes" << endl;
  else cout << "No" << endl;
}
