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
 */
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);
        abc134_b solver = new abc134_b();
        solver.solve(1, in, out);
        out.close();
    }

    static class abc134_b {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        }

    }
}
 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);
        abc134_b solver = new abc134_b();
        solver.solve(1, in, out);
        out.close();
    }

    static class abc134_b {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        }

    }
} 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);
        abc134_b solver = new abc134_b();
        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);
        abc134_b solver = new abc134_b();
        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) abc134_b solver = new abc134_b(); solver new abc134_b() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class abc134_b {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        }

    } abc134_b public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        } solve {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        } int N = in.nextInt(); N in.nextInt() in.nextInt in int D = in.nextInt(); D in.nextInt() in.nextInt in int mans = (int) Math.ceil(N / ((D * 2) + 1)); mans (int) Math.ceil(N / ((D * 2) + 1)) Math.ceil Math N / ((D * 2) + 1) N ((D * 2) + 1) (D * 2) D 2 1 if (N % ((D * 2) + 1) != 0) {
                mans++;
            } N % ((D * 2) + 1) != 0 N % ((D * 2) + 1) N ((D * 2) + 1) (D * 2) D 2 1 0 {
                mans++;
            } mans++ mans out.println(mans) out.println out mans 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);
        abc134_b solver = new abc134_b();
        solver.solve(1, in, out);
        out.close();
    }

    static class abc134_b {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        }

    }
} 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);
        abc134_b solver = new abc134_b();
        solver.solve(1, in, out);
        out.close();
    }

    static class abc134_b {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        }

    }
} 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
 */
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);
        abc134_b solver = new abc134_b();
        solver.solve(1, in, out);
        out.close();
    }

    static class abc134_b {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            int D = in.nextInt();

            int mans = (int) Math.ceil(N / ((D * 2) + 1));
            if (N % ((D * 2) + 1) != 0) {
                mans++;
            }
            out.println(mans);

        }

    }
}

