#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main(){
  int a, b, c, d;
  cin >> a >> b >> c >> d;
  int t_hp = (a-1) / d;
  int a_hp = (c-1) / b;
  if (t_hp >= a_hp) cout << "Yes" << endl;
  else cout << "No" << endl;
}