import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int D = scanner.nextInt();

    int observedRange = D * 2 + 1;
    int answer;
    if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    }

    System.out.println(answer);

  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int D = scanner.nextInt();

    int observedRange = D * 2 + 1;
    int answer;
    if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    }

    System.out.println(answer);

  }
} Main public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int D = scanner.nextInt();

    int observedRange = D * 2 + 1;
    int answer;
    if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    }

    System.out.println(answer);

  } main {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int D = scanner.nextInt();

    int observedRange = D * 2 + 1;
    int answer;
    if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    }

    System.out.println(answer);

  } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int N = scanner.nextInt(); N scanner.nextInt() scanner.nextInt scanner int D = scanner.nextInt(); D scanner.nextInt() scanner.nextInt scanner int observedRange = D * 2 + 1; observedRange D * 2 + 1 D * 2 D 2 1 int answer; answer if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    } N % observedRange == 0 N % observedRange N observedRange 0 {
      answer = N / observedRange;
    } answer = N / observedRange answer N / observedRange N observedRange {
      answer = N / observedRange + 1;
    } answer = N / observedRange + 1 answer N / observedRange + 1 N / observedRange N observedRange 1 System.out.println(answer) System.out.println System.out System System.out answer String[] args args public class Main {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int D = scanner.nextInt();

    int observedRange = D * 2 + 1;
    int answer;
    if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    }

    System.out.println(answer);

  }
} public class Main {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int D = scanner.nextInt();

    int observedRange = D * 2 + 1;
    int answer;
    if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    }

    System.out.println(answer);

  }
} Main
import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int N = scanner.nextInt();
    int D = scanner.nextInt();

    int observedRange = D * 2 + 1;
    int answer;
    if (N % observedRange == 0) {
      answer = N / observedRange;
    } else {
      answer = N / observedRange + 1;
    }

    System.out.println(answer);

  }
}