import java.awt.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
import java.util.List;

public class Main {
    public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextInt();
        double d=sc.nextInt();
        int x=(int)Math.ceil(n/(2d*d+1d));
        System.out.println(x);

    }

}
 import java.awt.*; awt.* java import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.*; util.* java import java.util.List; List java.util public class Main {
    public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextInt();
        double d=sc.nextInt();
        int x=(int)Math.ceil(n/(2d*d+1d));
        System.out.println(x);

    }

} Main public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextInt();
        double d=sc.nextInt();
        int x=(int)Math.ceil(n/(2d*d+1d));
        System.out.println(x);

    } main {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextInt();
        double d=sc.nextInt();
        int x=(int)Math.ceil(n/(2d*d+1d));
        System.out.println(x);

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double n=sc.nextInt(); n sc.nextInt() sc.nextInt sc double d=sc.nextInt(); d sc.nextInt() sc.nextInt sc int x=(int)Math.ceil(n/(2d*d+1d)); x (int)Math.ceil(n/(2d*d+1d)) Math.ceil Math n/(2d*d+1d) n (2d*d+1d) 2d*d 2d d 1d System.out.println(x) System.out.println System.out System System.out x String args[] args public class Main {
    public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextInt();
        double d=sc.nextInt();
        int x=(int)Math.ceil(n/(2d*d+1d));
        System.out.println(x);

    }

} public class Main {
    public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextInt();
        double d=sc.nextInt();
        int x=(int)Math.ceil(n/(2d*d+1d));
        System.out.println(x);

    }

} Main
import java.awt.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
import java.util.List;

public class Main {
    public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextInt();
        double d=sc.nextInt();
        int x=(int)Math.ceil(n/(2d*d+1d));
        System.out.println(x);

    }

}

