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

int main () {
  int A, B, C, D;
  cin >> A >> B >> C >> D;
  int attack;
  if (C%B == 0) attack = C/B-1;
  else attack = C/B;
  if (A <= D*attack) cout << "No" << endl;
  else cout << "Yes" << endl;
}