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

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans = 0;
    int able = 2 * d + 1;
    for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
} import java.util.*; util.* java import java.io.*; io.* 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 ans = 0;
    int able = 2 * d + 1;
    for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans = 0;
    int able = 2 * d + 1;
    for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans = 0;
    int able = 2 * d + 1;
    for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  } 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 ans = 0; ans 0 int able = 2 * d + 1; able 2 * d + 1 2 * d 2 d 1 for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    } int i = 1; int i = 1; i 1 i < 20 i 20 i++ i++ i {
      if (i * able >= n) {
        ans = i;
        break;
      }
    } {
      if (i * able >= n) {
        ans = i;
        break;
      }
    } if (i * able >= n) {
        ans = i;
        break;
      } i * able >= n i * able i able n {
        ans = i;
        break;
      } ans = i ans i break; System.out.println(ans) System.out.println System.out System System.out ans 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 ans = 0;
    int able = 2 * d + 1;
    for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans = 0;
    int able = 2 * d + 1;
    for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
} Main
import java.util.*;
import java.io.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans = 0;
    int able = 2 * d + 1;
    for(int i = 1; i < 20; i++){
      if (i * able >= n) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
}