#include<iostream>
using namespace std;

int main()
{
  	bool flag = true;
 	int a,b,c,d;
  	cin >> a >> b >> c >> d;
  	while(true)
    {
      	c -= b;
      	if(c <= 0)
        {
          flag = false;
          break;
        }
      	a -= d;
      	if(a <= 0)
        {
          flag = true;
          break;
        }
    }

  	if(flag)
      cout << "No";
  	else cout << "Yes";
}
