import java.util.*;

public class Main {
    public static void main(String[] args){
        Scanner sc  = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        println((int)Math.ceil((double)N/(D*2+1)));
    }

    static void println(Object o){
        System.out.println(o);
    }
    static void print(Object o){
        System.out.print(o);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args){
        Scanner sc  = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        println((int)Math.ceil((double)N/(D*2+1)));
    }

    static void println(Object o){
        System.out.println(o);
    }
    static void print(Object o){
        System.out.print(o);
    }
} Main public static void main(String[] args){
        Scanner sc  = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        println((int)Math.ceil((double)N/(D*2+1)));
    } main {
        Scanner sc  = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        println((int)Math.ceil((double)N/(D*2+1)));
    } 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 println((int)Math.ceil((double)N/(D*2+1))) println (int)Math.ceil((double)N/(D*2+1)) Math.ceil Math (double)N/(D*2+1) (double)N (D*2+1) D*2 D 2 1 String[] args args static void println(Object o){
        System.out.println(o);
    } println {
        System.out.println(o);
    } System.out.println(o) System.out.println System.out System System.out o Object o o static void print(Object o){
        System.out.print(o);
    } print {
        System.out.print(o);
    } System.out.print(o) System.out.print System.out System System.out o Object o o public class Main {
    public static void main(String[] args){
        Scanner sc  = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        println((int)Math.ceil((double)N/(D*2+1)));
    }

    static void println(Object o){
        System.out.println(o);
    }
    static void print(Object o){
        System.out.print(o);
    }
} public class Main {
    public static void main(String[] args){
        Scanner sc  = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        println((int)Math.ceil((double)N/(D*2+1)));
    }

    static void println(Object o){
        System.out.println(o);
    }
    static void print(Object o){
        System.out.print(o);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args){
        Scanner sc  = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        println((int)Math.ceil((double)N/(D*2+1)));
    }

    static void println(Object o){
        System.out.println(o);
    }
    static void print(Object o){
        System.out.print(o);
    }
}
