#include <iostream>
using namespace std;

int main()
{
  int HT, ST, HA, SA;
  cin >> HT >> ST >> HA >> SA;
  int x = 1;
  while (1)
  {
    if (x == 1)
    {
      HA = HA - ST;
      if (HA <= 0)
      {
        cout << "Yes";
        return 0;
      }
      x = 0;
    }
    else if (x == 0)
    {
      HT = HT - SA;
      if (HT <= 0)
      {
        cout << "No";
        return 0;
      }
      x = 1;
    }
  }
}