import java.util.*;
class Main{
  public static void main(String[] args){
	Scanner stdIn = new Scanner(System.in);
	int N = stdIn.nextInt();
    int D = stdIn.nextInt();
    int a =D*2+1;
    int ans=N/a;
    if(N%a!=0){
      ans+=1;
    }
    System.out.println(ans);
  }
} import java.util.*; util.* java class Main{
  public static void main(String[] args){
	Scanner stdIn = new Scanner(System.in);
	int N = stdIn.nextInt();
    int D = stdIn.nextInt();
    int a =D*2+1;
    int ans=N/a;
    if(N%a!=0){
      ans+=1;
    }
    System.out.println(ans);
  }
} Main public static void main(String[] args){
	Scanner stdIn = new Scanner(System.in);
	int N = stdIn.nextInt();
    int D = stdIn.nextInt();
    int a =D*2+1;
    int ans=N/a;
    if(N%a!=0){
      ans+=1;
    }
    System.out.println(ans);
  } main {
	Scanner stdIn = new Scanner(System.in);
	int N = stdIn.nextInt();
    int D = stdIn.nextInt();
    int a =D*2+1;
    int ans=N/a;
    if(N%a!=0){
      ans+=1;
    }
    System.out.println(ans);
  } Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) int N = stdIn.nextInt(); N stdIn.nextInt() stdIn.nextInt stdIn int D = stdIn.nextInt(); D stdIn.nextInt() stdIn.nextInt stdIn int a =D*2+1; a D*2+1 D*2 D 2 1 int ans=N/a; ans N/a N a if(N%a!=0){
      ans+=1;
    } N%a!=0 N%a N a 0 {
      ans+=1;
    } ans+=1 ans 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;
class Main{
  public static void main(String[] args){
	Scanner stdIn = new Scanner(System.in);
	int N = stdIn.nextInt();
    int D = stdIn.nextInt();
    int a =D*2+1;
    int ans=N/a;
    if(N%a!=0){
      ans+=1;
    }
    System.out.println(ans);
  }
}