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

int main() {
  int T_HP, T_Attack, A_HP, A_Attack;
  cin >> T_HP >> T_Attack >> A_HP >> A_Attack;
  if((A_HP/T_Attack) > (T_HP/A_Attack))
    cout << "Yes" << endl;
  else cout << "No" << endl;
}
