import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        String[] line1 = line.split(" ");
        double n = Double.parseDouble(line1[0]);
        double d = Double.parseDouble(line1[1]);
        System.out.println((int)Math.ceil(n / (d * 2 + 1)));
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        String[] line1 = line.split(" ");
        double n = Double.parseDouble(line1[0]);
        double d = Double.parseDouble(line1[1]);
        System.out.println((int)Math.ceil(n / (d * 2 + 1)));
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        String[] line1 = line.split(" ");
        double n = Double.parseDouble(line1[0]);
        double d = Double.parseDouble(line1[1]);
        System.out.println((int)Math.ceil(n / (d * 2 + 1)));
    } main {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        String[] line1 = line.split(" ");
        double n = Double.parseDouble(line1[0]);
        double d = Double.parseDouble(line1[1]);
        System.out.println((int)Math.ceil(n / (d * 2 + 1)));
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String line = sc.nextLine(); line sc.nextLine() sc.nextLine sc String[] line1 = line.split(" "); line1 line.split(" ") line.split line " " double n = Double.parseDouble(line1[0]); n Double.parseDouble(line1[0]) Double.parseDouble Double line1[0] line1 0 double d = Double.parseDouble(line1[1]); d Double.parseDouble(line1[1]) Double.parseDouble Double line1[1] line1 1 System.out.println((int)Math.ceil(n / (d * 2 + 1))) System.out.println System.out System System.out (int)Math.ceil(n / (d * 2 + 1)) Math.ceil Math n / (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        String[] line1 = line.split(" ");
        double n = Double.parseDouble(line1[0]);
        double d = Double.parseDouble(line1[1]);
        System.out.println((int)Math.ceil(n / (d * 2 + 1)));
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        String[] line1 = line.split(" ");
        double n = Double.parseDouble(line1[0]);
        double d = Double.parseDouble(line1[1]);
        System.out.println((int)Math.ceil(n / (d * 2 + 1)));
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        String[] line1 = line.split(" ");
        double n = Double.parseDouble(line1[0]);
        double d = Double.parseDouble(line1[1]);
        System.out.println((int)Math.ceil(n / (d * 2 + 1)));
    }
}
