import java.util.Scanner;

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

    int kanshi = 2 * D + 1;

    if (N <= kanshi) {
      System.out.println(1);
      return;
    }

    int count = 0;

    while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    }
  }

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

    int kanshi = 2 * D + 1;

    if (N <= kanshi) {
      System.out.println(1);
      return;
    }

    int count = 0;

    while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    }
  }

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

    int kanshi = 2 * D + 1;

    if (N <= kanshi) {
      System.out.println(1);
      return;
    }

    int count = 0;

    while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    }
  } main {
    Scanner scan = new Scanner(System.in);
    int N = scan.nextInt();
    int D = scan.nextInt();

    int kanshi = 2 * D + 1;

    if (N <= kanshi) {
      System.out.println(1);
      return;
    }

    int count = 0;

    while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    }
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int N = scan.nextInt(); N scan.nextInt() scan.nextInt scan int D = scan.nextInt(); D scan.nextInt() scan.nextInt scan int kanshi = 2 * D + 1; kanshi 2 * D + 1 2 * D 2 D 1 if (N <= kanshi) {
      System.out.println(1);
      return;
    } N <= kanshi N kanshi {
      System.out.println(1);
      return;
    } System.out.println(1) System.out.println System.out System System.out 1 return; int count = 0; count 0 while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    } true {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    } count++ count N -= kanshi N kanshi if (N <= 0) {
        System.out.println(count);
        return;
      } N <= 0 N 0 {
        System.out.println(count);
        return;
      } System.out.println(count) System.out.println System.out System System.out count return; String[] args args public class Main {
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int N = scan.nextInt();
    int D = scan.nextInt();

    int kanshi = 2 * D + 1;

    if (N <= kanshi) {
      System.out.println(1);
      return;
    }

    int count = 0;

    while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    }
  }

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

    int kanshi = 2 * D + 1;

    if (N <= kanshi) {
      System.out.println(1);
      return;
    }

    int count = 0;

    while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    }
  }

} Main
import java.util.Scanner;

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

    int kanshi = 2 * D + 1;

    if (N <= kanshi) {
      System.out.println(1);
      return;
    }

    int count = 0;

    while (true) {
      count++;
      N -= kanshi;
      if (N <= 0) {
        System.out.println(count);
        return;
      }
    }
  }

}
