#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define int long long
#define _GLIBCXX_DEBUG

signed main() {
  int A, B, C, D; cin >> A >> B >> C >> D;
  while(true) {
    C-=B;
    if(C<=0) {
      cout << "Yes" << endl;
      return 0;
    }
    A-=D;
    if(A<=0) {
      cout << "No" << endl;
      return 0;
    }
  }

}