import java.io.*;
import java.util.*;

public class Main {

    public static void main(final String[] args) throws Exception {
        final Scanner sc = new Scanner(System.in);
        long N;
        N = sc.nextLong();
        long D;
        D = sc.nextLong();

        final Solver solver = new Solver();
        solver.solve(N, D);
    }
}

class Solver {
    public void solve(long N, long D) {
        System.out.println((int) Math.ceil(N / (2.0 * D + 1)));
    }
}
 import java.io.*; io.* java import java.util.*; util.* java public class Main {

    public static void main(final String[] args) throws Exception {
        final Scanner sc = new Scanner(System.in);
        long N;
        N = sc.nextLong();
        long D;
        D = sc.nextLong();

        final Solver solver = new Solver();
        solver.solve(N, D);
    }
} Main public static void main(final String[] args) throws Exception {
        final Scanner sc = new Scanner(System.in);
        long N;
        N = sc.nextLong();
        long D;
        D = sc.nextLong();

        final Solver solver = new Solver();
        solver.solve(N, D);
    } main {
        final Scanner sc = new Scanner(System.in);
        long N;
        N = sc.nextLong();
        long D;
        D = sc.nextLong();

        final Solver solver = new Solver();
        solver.solve(N, D);
    } final Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long N; N N = sc.nextLong() N sc.nextLong() sc.nextLong sc long D; D D = sc.nextLong() D sc.nextLong() sc.nextLong sc final Solver solver = new Solver(); solver new Solver() solver.solve(N, D) solver.solve solver N D final String[] args args class Solver {
    public void solve(long N, long D) {
        System.out.println((int) Math.ceil(N / (2.0 * D + 1)));
    }
} Solver public void solve(long N, long D) {
        System.out.println((int) Math.ceil(N / (2.0 * D + 1)));
    } solve {
        System.out.println((int) Math.ceil(N / (2.0 * D + 1)));
    } System.out.println((int) Math.ceil(N / (2.0 * D + 1))) System.out.println System.out System System.out (int) Math.ceil(N / (2.0 * D + 1)) Math.ceil Math N / (2.0 * D + 1) N (2.0 * D + 1) 2.0 * D 2.0 D 1 long N N long D D public class Main {

    public static void main(final String[] args) throws Exception {
        final Scanner sc = new Scanner(System.in);
        long N;
        N = sc.nextLong();
        long D;
        D = sc.nextLong();

        final Solver solver = new Solver();
        solver.solve(N, D);
    }
} public class Main {

    public static void main(final String[] args) throws Exception {
        final Scanner sc = new Scanner(System.in);
        long N;
        N = sc.nextLong();
        long D;
        D = sc.nextLong();

        final Solver solver = new Solver();
        solver.solve(N, D);
    }
} Main
import java.io.*;
import java.util.*;

public class Main {

    public static void main(final String[] args) throws Exception {
        final Scanner sc = new Scanner(System.in);
        long N;
        N = sc.nextLong();
        long D;
        D = sc.nextLong();

        final Solver solver = new Solver();
        solver.solve(N, D);
    }
}

class Solver {
    public void solve(long N, long D) {
        System.out.println((int) Math.ceil(N / (2.0 * D + 1)));
    }
}

