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

int main() {
  int a,b,aa,bb;
  cin >> a >> b >> aa >> bb;
  string c;
  for (bool i = true; i == true;) 
  {
    aa -= b;
    if (aa < 1)
    {
      c = "Yes";
      i = false;
    }
    a -= bb;
    if (a < 1)
    {
      c = "No";
      i = false;
    } 
  }
  cout << c << endl;
}