
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner stdin = new Scanner(System.in);
        int n = stdin.nextInt();
        int d = stdin.nextInt();
        
        int div = n / (d * 2 + 1);
        int mod = n % (d * 2 + 1);
        if (mod == 0) {
            System.out.println(div);
        } else {
            System.out.println(div + 1);
        }
    }

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

} Main public static void main(String[] args) {
        Scanner stdin = new Scanner(System.in);
        int n = stdin.nextInt();
        int d = stdin.nextInt();
        
        int div = n / (d * 2 + 1);
        int mod = n % (d * 2 + 1);
        if (mod == 0) {
            System.out.println(div);
        } else {
            System.out.println(div + 1);
        }
    } main {
        Scanner stdin = new Scanner(System.in);
        int n = stdin.nextInt();
        int d = stdin.nextInt();
        
        int div = n / (d * 2 + 1);
        int mod = n % (d * 2 + 1);
        if (mod == 0) {
            System.out.println(div);
        } else {
            System.out.println(div + 1);
        }
    } 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 div = n / (d * 2 + 1); div n / (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 int mod = n % (d * 2 + 1); mod n % (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 if (mod == 0) {
            System.out.println(div);
        } else {
            System.out.println(div + 1);
        } mod == 0 mod 0 {
            System.out.println(div);
        } System.out.println(div) System.out.println System.out System System.out div {
            System.out.println(div + 1);
        } System.out.println(div + 1) System.out.println System.out System System.out div + 1 div 1 String[] args args public class Main {
    public static void main(String[] args) {
        Scanner stdin = new Scanner(System.in);
        int n = stdin.nextInt();
        int d = stdin.nextInt();
        
        int div = n / (d * 2 + 1);
        int mod = n % (d * 2 + 1);
        if (mod == 0) {
            System.out.println(div);
        } else {
            System.out.println(div + 1);
        }
    }

} public class Main {
    public static void main(String[] args) {
        Scanner stdin = new Scanner(System.in);
        int n = stdin.nextInt();
        int d = stdin.nextInt();
        
        int div = n / (d * 2 + 1);
        int mod = n % (d * 2 + 1);
        if (mod == 0) {
            System.out.println(div);
        } else {
            System.out.println(div + 1);
        }
    }

} Main

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner stdin = new Scanner(System.in);
        int n = stdin.nextInt();
        int d = stdin.nextInt();
        
        int div = n / (d * 2 + 1);
        int mod = n % (d * 2 + 1);
        if (mod == 0) {
            System.out.println(div);
        } else {
            System.out.println(div + 1);
        }
    }

}
