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

int main() {
  int a, b, c, d;
  cin >> a >> b >> c >> d;
  while (a > 0) {
    c -= b;
    if (c <= 0) {
      cout << "Yes" << endl;
      break;
    }
    a -= d;
    if (a <= 0) {
      cout << "No" << endl;
    }
  }
}