import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.regex.*;
public class Main {
      private static final Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
     int n = scanner.nextInt();
      int d = scanner.nextInt();
      int x=2*d+1;int y=0;
      if(n%x==0)
        y=n/x;
      else
        y=n/x+1;
      System.out.print(y);
        

    }
} import java.io.*; io.* java import java.math.*; math.* java import java.security.*; security.* java import java.text.*; text.* java import java.util.*; util.* java import java.util.concurrent.*; concurrent.* java.util import java.util.regex.*; regex.* java.util public class Main {
      private static final Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
     int n = scanner.nextInt();
      int d = scanner.nextInt();
      int x=2*d+1;int y=0;
      if(n%x==0)
        y=n/x;
      else
        y=n/x+1;
      System.out.print(y);
        

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

    } main {
     int n = scanner.nextInt();
      int d = scanner.nextInt();
      int x=2*d+1;int y=0;
      if(n%x==0)
        y=n/x;
      else
        y=n/x+1;
      System.out.print(y);
        

    } int n = scanner.nextInt(); n scanner.nextInt() scanner.nextInt scanner int d = scanner.nextInt(); d scanner.nextInt() scanner.nextInt scanner int x=2*d+1; x 2*d+1 2*d 2 d 1 int y=0; y 0 if(n%x==0)
        y=n/x;
      else
        y=n/x+1; n%x==0 n%x n x 0 y=n/x y n/x n x y=n/x+1 y n/x+1 n/x n x 1 System.out.print(y) System.out.print System.out System System.out y String[] args args public class Main {
      private static final Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
     int n = scanner.nextInt();
      int d = scanner.nextInt();
      int x=2*d+1;int y=0;
      if(n%x==0)
        y=n/x;
      else
        y=n/x+1;
      System.out.print(y);
        

    }
} public class Main {
      private static final Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
     int n = scanner.nextInt();
      int d = scanner.nextInt();
      int x=2*d+1;int y=0;
      if(n%x==0)
        y=n/x;
      else
        y=n/x+1;
      System.out.print(y);
        

    }
} Main
import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.regex.*;
public class Main {
      private static final Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
     int n = scanner.nextInt();
      int d = scanner.nextInt();
      int x=2*d+1;int y=0;
      if(n%x==0)
        y=n/x;
      else
        y=n/x+1;
      System.out.print(y);
        

    }
}
