import java.util.*;

class Main{
  public static void main(String[] args){
    Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    int m=2*sc.nextInt()+1;
    System.out.println((n+m-1)/m);
  }
} import java.util.*; util.* java class Main{
  public static void main(String[] args){
    Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    int m=2*sc.nextInt()+1;
    System.out.println((n+m-1)/m);
  }
} Main public static void main(String[] args){
    Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    int m=2*sc.nextInt()+1;
    System.out.println((n+m-1)/m);
  } main {
    Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    int m=2*sc.nextInt()+1;
    System.out.println((n+m-1)/m);
  } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) int n=sc.nextInt(); n sc.nextInt() sc.nextInt sc int m=2*sc.nextInt()+1; m 2*sc.nextInt()+1 2*sc.nextInt() 2 sc.nextInt() sc.nextInt sc 1 System.out.println((n+m-1)/m) System.out.println System.out System System.out (n+m-1)/m (n+m-1) n+m n m 1 m String[] args args
import java.util.*;

class Main{
  public static void main(String[] args){
    Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    int m=2*sc.nextInt()+1;
    System.out.println((n+m-1)/m);
  }
}