#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  int A,B,C,D;
  cin >> A >> B >> C >> D;
  bool ans = true;
  while (0 == 0) {
    C = C - B;
    if (C <= 0) {
      ans = true;
      break;
    }
    A = A - D;
    if (A <= 0) {
      ans = false;
      break;
    }
  }
  if (ans) cout << "Yes" << endl;
  else cout << "No" << endl;
  return 0;
}