import java.util.Scanner;

public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dtmp = d;
    d++;
    int ans = 1;

    while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    }

    System.out.println(ans);

  }
} import java.util.Scanner; Scanner java.util public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dtmp = d;
    d++;
    int ans = 1;

    while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    }

    System.out.println(ans);

  }
} Main public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dtmp = d;
    d++;
    int ans = 1;

    while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    }

    System.out.println(ans);

  } main {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dtmp = d;
    d++;
    int ans = 1;

    while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    }

    System.out.println(ans);

  } 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 dtmp = d; dtmp d d++ d int ans = 1; ans 1 while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    } true {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    } d += (2 * dtmp) + 1 d (2 * dtmp) + 1 (2 * dtmp) 2 dtmp 1 if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      } (d - dtmp) <= n (d - dtmp) d dtmp n {
        ans++;
      } ans++ ans {
        break;
      } break; System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dtmp = d;
    d++;
    int ans = 1;

    while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    }

    System.out.println(ans);

  }
} public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dtmp = d;
    d++;
    int ans = 1;

    while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    }

    System.out.println(ans);

  }
} Main
import java.util.Scanner;

public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dtmp = d;
    d++;
    int ans = 1;

    while (true) {
      d += (2 * dtmp) + 1;
      if ((d - dtmp) <= n) {
        ans++;
      } else {
        break;
      }
    }

    System.out.println(ans);

  }
}