import java.util.Scanner;
 
public class Main { //クラス名はMain
    public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String n = scan.next();
    String d = scan.next();
    int N = Integer.parseInt(n);
    int D = Integer.parseInt(d);
    
    int ans = (N + 2*D) / (2*D +1);
    
    System.out.println(ans);
 
 
    }
} import java.util.Scanner; Scanner java.util public class Main { //クラス名はMain
    public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String n = scan.next();
    String d = scan.next();
    int N = Integer.parseInt(n);
    int D = Integer.parseInt(d);
    
    int ans = (N + 2*D) / (2*D +1);
    
    System.out.println(ans);
 
 
    }
} Main public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String n = scan.next();
    String d = scan.next();
    int N = Integer.parseInt(n);
    int D = Integer.parseInt(d);
    
    int ans = (N + 2*D) / (2*D +1);
    
    System.out.println(ans);
 
 
    } main {
    Scanner scan = new Scanner(System.in);
    String n = scan.next();
    String d = scan.next();
    int N = Integer.parseInt(n);
    int D = Integer.parseInt(d);
    
    int ans = (N + 2*D) / (2*D +1);
    
    System.out.println(ans);
 
 
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String n = scan.next(); n scan.next() scan.next scan String d = scan.next(); d scan.next() scan.next scan int N = Integer.parseInt(n); N Integer.parseInt(n) Integer.parseInt Integer n int D = Integer.parseInt(d); D Integer.parseInt(d) Integer.parseInt Integer d int ans = (N + 2*D) / (2*D +1); ans (N + 2*D) / (2*D +1) (N + 2*D) N 2*D 2 D (2*D +1) 2*D 2 D 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main { //クラス名はMain
    public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String n = scan.next();
    String d = scan.next();
    int N = Integer.parseInt(n);
    int D = Integer.parseInt(d);
    
    int ans = (N + 2*D) / (2*D +1);
    
    System.out.println(ans);
 
 
    }
} public class Main { //クラス名はMain
    public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String n = scan.next();
    String d = scan.next();
    int N = Integer.parseInt(n);
    int D = Integer.parseInt(d);
    
    int ans = (N + 2*D) / (2*D +1);
    
    System.out.println(ans);
 
 
    }
} Main
import java.util.Scanner;
 
public class Main { //クラス名はMain
    public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String n = scan.next();
    String d = scan.next();
    int N = Integer.parseInt(n);
    int D = Integer.parseInt(d);
    
    int ans = (N + 2*D) / (2*D +1);
    
    System.out.println(ans);
 
 
    }
}