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

int main(void)
{
  ios_base::sync_with_stdio(false);
  cin.tie(0); cout.tie(0);

  int A, B, C, D; cin >> A >> B >> C >> D;

  string ans;

  while (true) {
    C -= B; if (C <= 0) { ans = "Yes"; break; }
    A -= D; if (A <= 0) { ans = "No";  break; }
  }

  cout << ans << endl;

  return 0;
}
