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

int main()
{
  int A,B,C,D;
  string result;
  cin >> A >> B >> C >> D;

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

  cout << result << endl;
}