import java.util.*;
 
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        
        int n = sc.nextInt();
        int d = sc.nextInt();
        int f = d * 2 + 1;

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

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

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

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

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

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

        if (n % f == 0) {
            System.out.println(n / f);
        } else {
            System.out.println(n / f + 1);
        }
	}
}
