
import java.util.Scanner;

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

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

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

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

    } Scanner in = new Scanner(System.in); in new Scanner(System.in) int n= in.nextInt(); n in.nextInt() in.nextInt in int d= in.nextInt(); d in.nextInt() in.nextInt in int cover = d*2+1; cover d*2+1 d*2 d 2 1 int ans = n/cover; ans n/cover n cover if(n%cover==0)
            System.out.println(ans);
        else if(n>d && n%cover>0){
            ans++;
            System.out.println(ans);
        }
        else
            if(n<=d){
                System.out.println(1);
            } n%cover==0 n%cover n cover 0 System.out.println(ans) System.out.println System.out System System.out ans if(n>d && n%cover>0){
            ans++;
            System.out.println(ans);
        }
        else
            if(n<=d){
                System.out.println(1);
            } n>d && n%cover>0 n>d n d n%cover>0 n%cover n cover 0 {
            ans++;
            System.out.println(ans);
        } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans if(n<=d){
                System.out.println(1);
            } n<=d n d {
                System.out.println(1);
            } System.out.println(1) System.out.println System.out System System.out 1 String[] args args

import java.util.Scanner;

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

    }
}
