
import java.util.*;

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

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

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

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

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

import java.util.*;

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

        if(n % (2 * d + 1) == 0 )
        System.out.println(n / (2 * d + 1));
        else 
        System.out.println(n / (2 * d + 1) + 1);   
    }
}
