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