import java.util.Scanner;

public class Main{
    public static void main(String[] args){
        // 空白入力
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        // 空白入力
        int ans=0;
        while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        }
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main{
    public static void main(String[] args){
        // 空白入力
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        // 空白入力
        int ans=0;
        while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args){
        // 空白入力
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        // 空白入力
        int ans=0;
        while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        }
        System.out.println(ans);
    } main {
        // 空白入力
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        // 空白入力
        int ans=0;
        while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        }
        System.out.println(ans);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int d = scan.nextInt(); d scan.nextInt() scan.nextInt scan int ans=0; ans 0 while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        } n > 0 n 0 {
            ans++;
            n = n - (d * 2 + 1);
        } ans++ ans n = n - (d * 2 + 1) n n - (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main{
    public static void main(String[] args){
        // 空白入力
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        // 空白入力
        int ans=0;
        while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        }
        System.out.println(ans);
    }
} public class Main{
    public static void main(String[] args){
        // 空白入力
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        // 空白入力
        int ans=0;
        while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        }
        System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main{
    public static void main(String[] args){
        // 空白入力
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        // 空白入力
        int ans=0;
        while(n > 0){
            ans++;
            n = n - (d * 2 + 1);
        }
        System.out.println(ans);
    }
}
