import java.util.Scanner;
class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    //１人につき2d+1本の木を監視できる
    int a = n / (2*d + 1);
    int b = 0;
    if (n % (2*d + 1) != 0) {
      b = 1;
    }
    int c = a+b;
    System.out.println(c);
  }
} import java.util.Scanner; Scanner java.util class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    //１人につき2d+1本の木を監視できる
    int a = n / (2*d + 1);
    int b = 0;
    if (n % (2*d + 1) != 0) {
      b = 1;
    }
    int c = a+b;
    System.out.println(c);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    //１人につき2d+1本の木を監視できる
    int a = n / (2*d + 1);
    int b = 0;
    if (n % (2*d + 1) != 0) {
      b = 1;
    }
    int c = a+b;
    System.out.println(c);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    //１人につき2d+1本の木を監視できる
    int a = n / (2*d + 1);
    int b = 0;
    if (n % (2*d + 1) != 0) {
      b = 1;
    }
    int c = a+b;
    System.out.println(c);
  } 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 = n / (2*d + 1); a n / (2*d + 1) n (2*d + 1) 2*d 2 d 1 int b = 0; b 0 if (n % (2*d + 1) != 0) {
      b = 1;
    } n % (2*d + 1) != 0 n % (2*d + 1) n (2*d + 1) 2*d 2 d 1 0 {
      b = 1;
    } b = 1 b 1 int c = a+b; c a+b a b System.out.println(c) System.out.println System.out System System.out c String[] args args
import java.util.Scanner;
class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    //１人につき2d+1本の木を監視できる
    int a = n / (2*d + 1);
    int b = 0;
    if (n % (2*d + 1) != 0) {
      b = 1;
    }
    int c = a+b;
    System.out.println(c);
  }
}