import 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 dd = d * 2 + 1;

    double need = (double)n / dd;

    if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    }
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dd = d * 2 + 1;

    double need = (double)n / dd;

    if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    }
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dd = d * 2 + 1;

    double need = (double)n / dd;

    if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    }
  } main {
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dd = d * 2 + 1;

    double need = (double)n / dd;

    if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    }
  } 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 dd = d * 2 + 1; dd d * 2 + 1 d * 2 d 2 1 double need = (double)n / dd; need (double)n / dd (double)n dd if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    } n % dd == 0 n % dd n dd 0 {
      System.out.println((int)need);
    } System.out.println((int)need) System.out.println System.out System System.out (int)need {
      System.out.println((int)Math.ceil(need));
    } System.out.println((int)Math.ceil(need)) System.out.println System.out System System.out (int)Math.ceil(need) Math.ceil Math need 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 dd = d * 2 + 1;

    double need = (double)n / dd;

    if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    }
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int dd = d * 2 + 1;

    double need = (double)n / dd;

    if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    }
  }
} Main
import 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 dd = d * 2 + 1;

    double need = (double)n / dd;

    if(n % dd == 0) {
      System.out.println((int)need);
    } else {
      System.out.println((int)Math.ceil(need));
    }
  }
}
