

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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    }
} import java.io.*; io.* java import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int trees = sc.nextInt(); trees sc.nextInt() sc.nextInt sc int inspector = sc.nextInt(); inspector sc.nextInt() sc.nextInt sc int a = 2*inspector + 1; a 2*inspector + 1 2*inspector 2 inspector 1 int ans = 0; ans 0 if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        } trees % a == 0 trees % a trees a 0 {
            ans = trees /a;
        } ans = trees /a ans trees /a trees a {
            ans = (trees/a) + 1;
        } ans = (trees/a) + 1 ans (trees/a) + 1 (trees/a) trees a 1 System.out.print(ans) System.out.print System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    }
} Main


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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    }
}