import java.io.InputStream;
import java.io.PrintStream;
import java.util.*;

public class Main {

  public static void main(String[] args) {
    solve(System.in, System.out);
  }

  static void solve(InputStream is, PrintStream os) {
    Scanner sc = new Scanner(is);

    /* read */
    int n = sc.nextInt();
    int d = sc.nextInt();

    int div = 2 * d + 1;

    int ans = 0;
    if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    }

    os.println(ans);
  }
} import java.io.InputStream; InputStream java.io import java.io.PrintStream; PrintStream java.io import java.util.*; util.* java public class Main {

  public static void main(String[] args) {
    solve(System.in, System.out);
  }

  static void solve(InputStream is, PrintStream os) {
    Scanner sc = new Scanner(is);

    /* read */
    int n = sc.nextInt();
    int d = sc.nextInt();

    int div = 2 * d + 1;

    int ans = 0;
    if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    }

    os.println(ans);
  }
} Main public static void main(String[] args) {
    solve(System.in, System.out);
  } main {
    solve(System.in, System.out);
  } solve(System.in, System.out) solve System.in System System.in System.out System System.out String[] args args static void solve(InputStream is, PrintStream os) {
    Scanner sc = new Scanner(is);

    /* read */
    int n = sc.nextInt();
    int d = sc.nextInt();

    int div = 2 * d + 1;

    int ans = 0;
    if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    }

    os.println(ans);
  } solve {
    Scanner sc = new Scanner(is);

    /* read */
    int n = sc.nextInt();
    int d = sc.nextInt();

    int div = 2 * d + 1;

    int ans = 0;
    if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    }

    os.println(ans);
  } Scanner sc = new Scanner(is); sc new Scanner(is) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc int div = 2 * d + 1; div 2 * d + 1 2 * d 2 d 1 int ans = 0; ans 0 if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    } n % div == 0 n % div n div 0 {
      ans = n / div;
    } ans = n / div ans n / div n div {
      ans = n / div + 1;
    } ans = n / div + 1 ans n / div + 1 n / div n div 1 os.println(ans) os.println os ans InputStream is is PrintStream os os public class Main {

  public static void main(String[] args) {
    solve(System.in, System.out);
  }

  static void solve(InputStream is, PrintStream os) {
    Scanner sc = new Scanner(is);

    /* read */
    int n = sc.nextInt();
    int d = sc.nextInt();

    int div = 2 * d + 1;

    int ans = 0;
    if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    }

    os.println(ans);
  }
} public class Main {

  public static void main(String[] args) {
    solve(System.in, System.out);
  }

  static void solve(InputStream is, PrintStream os) {
    Scanner sc = new Scanner(is);

    /* read */
    int n = sc.nextInt();
    int d = sc.nextInt();

    int div = 2 * d + 1;

    int ans = 0;
    if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    }

    os.println(ans);
  }
} Main
import java.io.InputStream;
import java.io.PrintStream;
import java.util.*;

public class Main {

  public static void main(String[] args) {
    solve(System.in, System.out);
  }

  static void solve(InputStream is, PrintStream os) {
    Scanner sc = new Scanner(is);

    /* read */
    int n = sc.nextInt();
    int d = sc.nextInt();

    int div = 2 * d + 1;

    int ans = 0;
    if (n % div == 0) {
      ans = n / div;
    } else {
      ans = n / div + 1;
    }

    os.println(ans);
  }
}