import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Abhijeetkns
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BGoldenApple solver = new BGoldenApple();
        solver.solve(1, in, out);
        out.close();
    }

    static class BGoldenApple {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BGoldenApple solver = new BGoldenApple();
        solver.solve(1, in, out);
        out.close();
    }

    static class BGoldenApple {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BGoldenApple solver = new BGoldenApple();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BGoldenApple solver = new BGoldenApple();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) BGoldenApple solver = new BGoldenApple(); solver new BGoldenApple() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class BGoldenApple {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        }

    } BGoldenApple public void solve(int testNumber, Scanner in, PrintWriter out) {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        } solve {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        } double n = in.nextDouble(); n in.nextDouble() in.nextDouble in double d = in.nextDouble(); d in.nextDouble() in.nextDouble in d = 2 * d + 1 d 2 * d + 1 2 * d 2 d 1 out.println((int) Math.ceil(n / d)) out.println out (int) Math.ceil(n / d) Math.ceil Math n / d n d int testNumber testNumber Scanner in in PrintWriter out out public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BGoldenApple solver = new BGoldenApple();
        solver.solve(1, in, out);
        out.close();
    }

    static class BGoldenApple {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BGoldenApple solver = new BGoldenApple();
        solver.solve(1, in, out);
        out.close();
    }

    static class BGoldenApple {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Abhijeetkns
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BGoldenApple solver = new BGoldenApple();
        solver.solve(1, in, out);
        out.close();
    }

    static class BGoldenApple {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            double n = in.nextDouble();
            double d = in.nextDouble();
            d = 2 * d + 1;
            out.println((int) Math.ceil(n / d));
        }

    }
}

