import java.util.*;
import java.lang.*;

import static java.lang.StrictMath.abs;

class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        if((n) %(2*d+1)>0){
            System.out.println(n/((2*d)+1)+1);
        }else {

            System.out.println(n / (2 * d+1));
        }
    }
} import java.util.*; util.* java import java.lang.*; lang.* java import static java.lang.StrictMath.abs; import static java.lang.StrictMath.abs; import static java.lang.StrictMath.abs; class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        if((n) %(2*d+1)>0){
            System.out.println(n/((2*d)+1)+1);
        }else {

            System.out.println(n / (2 * d+1));
        }
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        if((n) %(2*d+1)>0){
            System.out.println(n/((2*d)+1)+1);
        }else {

            System.out.println(n / (2 * d+1));
        }
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        if((n) %(2*d+1)>0){
            System.out.println(n/((2*d)+1)+1);
        }else {

            System.out.println(n / (2 * d+1));
        }
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc if((n) %(2*d+1)>0){
            System.out.println(n/((2*d)+1)+1);
        }else {

            System.out.println(n / (2 * d+1));
        } (n) %(2*d+1)>0 (n) %(2*d+1) (n) (2*d+1) 2*d 2 d 1 0 {
            System.out.println(n/((2*d)+1)+1);
        } System.out.println(n/((2*d)+1)+1) System.out.println System.out System System.out n/((2*d)+1)+1 n/((2*d)+1) n ((2*d)+1) (2*d) 2 d 1 1 {

            System.out.println(n / (2 * d+1));
        } System.out.println(n / (2 * d+1)) System.out.println System.out System System.out n / (2 * d+1) n (2 * d+1) 2 * d 2 d 1 String[] args args
import java.util.*;
import java.lang.*;

import static java.lang.StrictMath.abs;

class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        if((n) %(2*d+1)>0){
            System.out.println(n/((2*d)+1)+1);
        }else {

            System.out.println(n / (2 * d+1));
        }
    }
}
