#include<iostream>
using namespace std;
int main()
{
	int v,t,s,d,s1,s2;
	cin>>v>>t>>s>>d;
	s1=t*v;
	s2=v*s;
	
	if(d>=s1&&d<=s2)	
		cout<<"No";
	else
		cout<<"Yes";	 


 return 0;
}

#include <iostream>
using namespace std;


int main()
{
  int a[4];
  char flag = 0;
  cin >> a[0] >> a[1] >> a[2] >> a[3];

  int sum = 0;
  for (int i = 0; i < 4; i++) {
    sum += a[i];
  }

  bool find = false;
  if (sum % 2 == 0)
  {
    for (int i = 0; i < 8; i++)
    {
      int sub = a[3];
      if ((i & (1 << 0)) != 0)
        sub += a[0];
      if ((i & (1 << 1)) != 0)
        sub += a[1];
      if ((i & (1 << 2)) != 0)
        sub += a[2];
      if (sub * 2 == sum)
        find = true;
      if (find)break;
    }
  }

  if (find)
  {
    cout << "Yes";
  }
  else
  {
    cout << "No";
  }

  return 0;
}