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 count = 1;
    while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    }
  }
} 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 count = 1;
    while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    }
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int count = 1;
    while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    }
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int count = 1;
    while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    }
  } 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 count = 1; count 1 while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    } true {
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    } if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;} count*(2*d+1) >= n count*(2*d+1) count (2*d+1) 2*d 2 d 1 n {
        System.out.println(count);
        break;
      } System.out.println(count) System.out.println System.out System System.out count break; {
        count++;} count++ count 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 count = 1;
    while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    }
  }
} public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int count = 1;
    while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    }
  }
} 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 count = 1;
    while(true){
      if(count*(2*d+1) >= n){
        System.out.println(count);
        break;
      } else {
        count++;}
    }
  }
}