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

int main() {
  int a,b,c,d;
  cin >> a >> b >> c >> d;

  bool flag = false;

  while(flag == false){
    c = c-b;
    if(c <= 0){
      cout << "Yes" << endl;
      break;
    }

    a = a-d;
    if(a <= 0){
      cout << "No" << endl;
      break;
    }
  }
}
