import java.util.Scanner;

class Main{
	public static void main(String[] args){
     	Scanner sc = new Scanner(System.in);
      	String s = sc.nextLine();
      	String[] spl = s.split(" ");
      	int N = Integer.parseInt(spl[0]);
      	int D = Integer.parseInt(spl[1]);
      	int ans = N / (D * 2 + 1);
      	int mod = N % (D * 2 + 1);
      	if(mod == 0){
      		System.out.println(ans);
        }else{
          	System.out.println(ans + 1);
        }
    }
} import java.util.Scanner; Scanner java.util class Main{
	public static void main(String[] args){
     	Scanner sc = new Scanner(System.in);
      	String s = sc.nextLine();
      	String[] spl = s.split(" ");
      	int N = Integer.parseInt(spl[0]);
      	int D = Integer.parseInt(spl[1]);
      	int ans = N / (D * 2 + 1);
      	int mod = N % (D * 2 + 1);
      	if(mod == 0){
      		System.out.println(ans);
        }else{
          	System.out.println(ans + 1);
        }
    }
} Main public static void main(String[] args){
     	Scanner sc = new Scanner(System.in);
      	String s = sc.nextLine();
      	String[] spl = s.split(" ");
      	int N = Integer.parseInt(spl[0]);
      	int D = Integer.parseInt(spl[1]);
      	int ans = N / (D * 2 + 1);
      	int mod = N % (D * 2 + 1);
      	if(mod == 0){
      		System.out.println(ans);
        }else{
          	System.out.println(ans + 1);
        }
    } main {
     	Scanner sc = new Scanner(System.in);
      	String s = sc.nextLine();
      	String[] spl = s.split(" ");
      	int N = Integer.parseInt(spl[0]);
      	int D = Integer.parseInt(spl[1]);
      	int ans = N / (D * 2 + 1);
      	int mod = N % (D * 2 + 1);
      	if(mod == 0){
      		System.out.println(ans);
        }else{
          	System.out.println(ans + 1);
        }
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.nextLine(); s sc.nextLine() sc.nextLine sc String[] spl = s.split(" "); spl s.split(" ") s.split s " " int N = Integer.parseInt(spl[0]); N Integer.parseInt(spl[0]) Integer.parseInt Integer spl[0] spl 0 int D = Integer.parseInt(spl[1]); D Integer.parseInt(spl[1]) Integer.parseInt Integer spl[1] spl 1 int ans = N / (D * 2 + 1); ans N / (D * 2 + 1) N (D * 2 + 1) D * 2 D 2 1 int mod = N % (D * 2 + 1); mod N % (D * 2 + 1) N (D * 2 + 1) D * 2 D 2 1 if(mod == 0){
      		System.out.println(ans);
        }else{
          	System.out.println(ans + 1);
        } mod == 0 mod 0 {
      		System.out.println(ans);
        } System.out.println(ans) System.out.println System.out System System.out ans {
          	System.out.println(ans + 1);
        } System.out.println(ans + 1) System.out.println System.out System System.out ans + 1 ans 1 String[] args args
import java.util.Scanner;

class Main{
	public static void main(String[] args){
     	Scanner sc = new Scanner(System.in);
      	String s = sc.nextLine();
      	String[] spl = s.split(" ");
      	int N = Integer.parseInt(spl[0]);
      	int D = Integer.parseInt(spl[1]);
      	int ans = N / (D * 2 + 1);
      	int mod = N % (D * 2 + 1);
      	if(mod == 0){
      		System.out.println(ans);
        }else{
          	System.out.println(ans + 1);
        }
    }
}