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();
        System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1);
    }
} 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();
        System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 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 System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1) System.out.println System.out System System.out N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1 N % ((2 * D) + 1) == 0 N % ((2 * D) + 1) N ((2 * D) + 1) (2 * D) 2 D 1 0 N / ((2 * D) + 1) N ((2 * D) + 1) (2 * D) 2 D 1 N / ((2 * D) + 1) + 1 N / ((2 * D) + 1) N ((2 * D) + 1) (2 * D) 2 D 1 1 String[] args args public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1);
    }
} public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1);
    }
} 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();
        System.out.println(N % ((2 * D) + 1) == 0 ? N / ((2 * D) + 1) : N / ((2 * D) + 1) + 1);
    }
}
