#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    long long n,k,temp;
	cin>>n>>k;
	  temp=(2*k)+1;
	  if(n%temp>=(k+1))
	  {
	  	cout<<(n/temp)+1;
	  }
	  else if(n%temp==0)
	  {
	  	cout<<n/temp;
	  }
    return 0;
}