import java.util.*;
public class Main{
    public static void main(String sp[]){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
		int d = sc.nextInt();
		int val = (2*d)+1;
		int div = n/val;
		int mod = n%val;
		if(mod>0)
			div+=1;
		System.out.println(div);
	}
} import java.util.*; util.* java public class Main{
    public static void main(String sp[]){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
		int d = sc.nextInt();
		int val = (2*d)+1;
		int div = n/val;
		int mod = n%val;
		if(mod>0)
			div+=1;
		System.out.println(div);
	}
} Main public static void main(String sp[]){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
		int d = sc.nextInt();
		int val = (2*d)+1;
		int div = n/val;
		int mod = n%val;
		if(mod>0)
			div+=1;
		System.out.println(div);
	} main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
		int d = sc.nextInt();
		int val = (2*d)+1;
		int div = n/val;
		int mod = n%val;
		if(mod>0)
			div+=1;
		System.out.println(div);
	} 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 val = (2*d)+1; val (2*d)+1 (2*d) 2 d 1 int div = n/val; div n/val n val int mod = n%val; mod n%val n val if(mod>0)
			div+=1; mod>0 mod 0 div+=1 div 1 System.out.println(div) System.out.println System.out System System.out div String sp[] sp public class Main{
    public static void main(String sp[]){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
		int d = sc.nextInt();
		int val = (2*d)+1;
		int div = n/val;
		int mod = n%val;
		if(mod>0)
			div+=1;
		System.out.println(div);
	}
} public class Main{
    public static void main(String sp[]){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
		int d = sc.nextInt();
		int val = (2*d)+1;
		int div = n/val;
		int mod = n%val;
		if(mod>0)
			div+=1;
		System.out.println(div);
	}
} Main
import java.util.*;
public class Main{
    public static void main(String sp[]){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
		int d = sc.nextInt();
		int val = (2*d)+1;
		int div = n/val;
		int mod = n%val;
		if(mod>0)
			div+=1;
		System.out.println(div);
	}
}