import java.util.*;
import java.math.*;
import java.io.*;


public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int d = sc.nextInt();

        int ans = n / (2 * d + 1) + (n%(2 * d + 1)!=0?1:0);
        System.out.println(ans);
    } 
} import java.util.*; util.* java import java.math.*; math.* java import java.io.*; io.* java public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int d = sc.nextInt();

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

        int ans = n / (2 * d + 1) + (n%(2 * d + 1)!=0?1:0);
        System.out.println(ans);
    } main {
        int n = sc.nextInt();
        int d = sc.nextInt();

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

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

        int ans = n / (2 * d + 1) + (n%(2 * d + 1)!=0?1:0);
        System.out.println(ans);
    } 
} Main
import java.util.*;
import java.math.*;
import java.io.*;


public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int d = sc.nextInt();

        int ans = n / (2 * d + 1) + (n%(2 * d + 1)!=0?1:0);
        System.out.println(ans);
    } 
}