import java.util.*;

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

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