import java.util.Scanner;
 
public class Main {
    static Scanner stdIn = new Scanner(System.in);
    public static void main(String[] args){
        int n = stdIn.nextInt();
        int d = stdIn.nextInt();

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

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

        System.out.println((int)Math.ceil((double)n / (2 * d + 1)));
    } main {
        int n = stdIn.nextInt();
        int d = stdIn.nextInt();

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

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

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

        System.out.println((int)Math.ceil((double)n / (2 * d + 1)));
    }
}