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

public class Main {

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

  static void resolve(InputStream is, PrintStream pw) {
    Scanner sc = new Scanner(is);
    long n = Integer.parseInt(sc.next());
    long d = Integer.parseInt(sc.next());
    long range = d * 2 + 1;
    long div = n / range;
    long ans;
    if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    }
    pw.println(ans);
  }
} import java.io.InputStream; InputStream java.io import java.io.PrintStream; PrintStream java.io import java.util.Scanner; Scanner java.util public class Main {

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

  static void resolve(InputStream is, PrintStream pw) {
    Scanner sc = new Scanner(is);
    long n = Integer.parseInt(sc.next());
    long d = Integer.parseInt(sc.next());
    long range = d * 2 + 1;
    long div = n / range;
    long ans;
    if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    }
    pw.println(ans);
  }
} Main public static void main(String[] args) {
    resolve(System.in, System.out);
  } main {
    resolve(System.in, System.out);
  } resolve(System.in, System.out) resolve System.in System System.in System.out System System.out String[] args args static void resolve(InputStream is, PrintStream pw) {
    Scanner sc = new Scanner(is);
    long n = Integer.parseInt(sc.next());
    long d = Integer.parseInt(sc.next());
    long range = d * 2 + 1;
    long div = n / range;
    long ans;
    if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    }
    pw.println(ans);
  } resolve {
    Scanner sc = new Scanner(is);
    long n = Integer.parseInt(sc.next());
    long d = Integer.parseInt(sc.next());
    long range = d * 2 + 1;
    long div = n / range;
    long ans;
    if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    }
    pw.println(ans);
  } Scanner sc = new Scanner(is); sc new Scanner(is) long n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc long d = Integer.parseInt(sc.next()); d Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc long range = d * 2 + 1; range d * 2 + 1 d * 2 d 2 1 long div = n / range; div n / range n range long ans; ans if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    } n % range == 0 n % range n range 0 {
      ans = div;
    } ans = div ans div {
      ans = div + 1;
    } ans = div + 1 ans div + 1 div 1 pw.println(ans) pw.println pw ans InputStream is is PrintStream pw pw public class Main {

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

  static void resolve(InputStream is, PrintStream pw) {
    Scanner sc = new Scanner(is);
    long n = Integer.parseInt(sc.next());
    long d = Integer.parseInt(sc.next());
    long range = d * 2 + 1;
    long div = n / range;
    long ans;
    if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    }
    pw.println(ans);
  }
} public class Main {

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

  static void resolve(InputStream is, PrintStream pw) {
    Scanner sc = new Scanner(is);
    long n = Integer.parseInt(sc.next());
    long d = Integer.parseInt(sc.next());
    long range = d * 2 + 1;
    long div = n / range;
    long ans;
    if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    }
    pw.println(ans);
  }
} Main
import java.io.InputStream;
import java.io.PrintStream;
import java.util.Scanner;

public class Main {

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

  static void resolve(InputStream is, PrintStream pw) {
    Scanner sc = new Scanner(is);
    long n = Integer.parseInt(sc.next());
    long d = Integer.parseInt(sc.next());
    long range = d * 2 + 1;
    long div = n / range;
    long ans;
    if (n % range == 0) {
      ans = div;
    } else {
      ans = div + 1;
    }
    pw.println(ans);
  }
}
