import java.util.*;
import java.io.*;

class Main {
  public static void main(String[] args){
    Scanner  sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = 0;
    int i = 0;
    while(a < n){
      a += 2 * d + 1;
      i ++;
          }
          System.out.println(i);
  }
} import java.util.*; util.* java import java.io.*; io.* java class Main {
  public static void main(String[] args){
    Scanner  sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = 0;
    int i = 0;
    while(a < n){
      a += 2 * d + 1;
      i ++;
          }
          System.out.println(i);
  }
} Main public static void main(String[] args){
    Scanner  sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = 0;
    int i = 0;
    while(a < n){
      a += 2 * d + 1;
      i ++;
          }
          System.out.println(i);
  } main {
    Scanner  sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = 0;
    int i = 0;
    while(a < n){
      a += 2 * d + 1;
      i ++;
          }
          System.out.println(i);
  } 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 a = 0; a 0 int i = 0; i 0 while(a < n){
      a += 2 * d + 1;
      i ++;
          } a < n a n {
      a += 2 * d + 1;
      i ++;
          } a += 2 * d + 1 a 2 * d + 1 2 * d 2 d 1 i ++ i System.out.println(i) System.out.println System.out System System.out i String[] args args
import java.util.*;
import java.io.*;

class Main {
  public static void main(String[] args){
    Scanner  sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = 0;
    int i = 0;
    while(a < n){
      a += 2 * d + 1;
      i ++;
          }
          System.out.println(i);
  }
}
