import java.util.Scanner;

public class Main {

   void solve() {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        int tmp = N / (2*D + 1);
        int ans = 0;
        if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        }

        System.out.print(ans);

    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
}
 import java.util.Scanner; Scanner java.util public class Main {

   void solve() {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        int tmp = N / (2*D + 1);
        int ans = 0;
        if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        }

        System.out.print(ans);

    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
} Main void solve() {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        int tmp = N / (2*D + 1);
        int ans = 0;
        if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        }

        System.out.print(ans);

    } solve {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        int tmp = N / (2*D + 1);
        int ans = 0;
        if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        }

        System.out.print(ans);

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc int tmp = N / (2*D + 1); tmp N / (2*D + 1) N (2*D + 1) 2*D 2 D 1 int ans = 0; ans 0 if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        } N % (2*D + 1) == 0 N % (2*D + 1) N (2*D + 1) 2*D 2 D 1 0 {
            ans = tmp;
        } ans = tmp ans tmp {
            ans = tmp + 1;
        } ans = tmp + 1 ans tmp + 1 tmp 1 System.out.print(ans) System.out.print System.out System System.out ans // Main
    public static void main(String[] args) {
        new Main().solve();
    } main {
        new Main().solve();
    } new Main().solve() new Main().solve new Main() String[] args args public class Main {

   void solve() {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        int tmp = N / (2*D + 1);
        int ans = 0;
        if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        }

        System.out.print(ans);

    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
} public class Main {

   void solve() {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        int tmp = N / (2*D + 1);
        int ans = 0;
        if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        }

        System.out.print(ans);

    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
} Main
import java.util.Scanner;

public class Main {

   void solve() {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        int tmp = N / (2*D + 1);
        int ans = 0;
        if (N % (2*D + 1) == 0) {
            ans = tmp;
        }
        else {
            ans = tmp + 1;
        }

        System.out.print(ans);

    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
}

