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

int main() {
  int A, B, C, D; cin >> A >> B >> C >> D;
  int a = (A - 1 + D) / D;
  int t = (C - 1 + B) / B;
  if (t <= a) cout << "Yes" << endl;
  else cout << "No" << endl; 
}

