#include <iostream>

using namespace std;

int main()
{
  int n,t,k,d;
  cin>>n>>t>>k>>d;
  if (2*t==2*d&&(n>!k)){
        cout<<"NO"<<endl;
    }else{
  if(n>k){

    if(2*t<=(t+d)){
        cout<<"YES"<<endl;
    }

  }
  else{
    cout<<"NO"<<endl;
  }
   }
    return 0;
}