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

int main() {
  int A, B, C, D;
  cin >> A >> B >> C >> D;

  while (A > 0) {
    C -= B;
    A -= D;
    if (C <= 0) {
      cout << "Yes" << endl;
    }
  }
  if ( C > 0) {
    cout << "No" << endl;
  }
}