import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        solve();
    }

    private static void solve() {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int d = input.nextInt();

        int ans = 0;

        while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        }

        System.out.println(ans);

    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        solve();
    }

    private static void solve() {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int d = input.nextInt();

        int ans = 0;

        while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        }

        System.out.println(ans);

    }
} Main public static void main(String[] args) {
        solve();
    } main {
        solve();
    } solve() solve String[] args args private static void solve() {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int d = input.nextInt();

        int ans = 0;

        while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        }

        System.out.println(ans);

    } solve {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int d = input.nextInt();

        int ans = 0;

        while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        }

        System.out.println(ans);

    } Scanner input = new Scanner(System.in); input new Scanner(System.in) int n = input.nextInt(); n input.nextInt() input.nextInt input int d = input.nextInt(); d input.nextInt() input.nextInt input int ans = 0; ans 0 while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        } n > 0 n 0 {
        	ans++;
        	n = n - 1 - 2*d;
        } ans++ ans n = n - 1 - 2*d n n - 1 - 2*d n - 1 - 2*d n 1 2*d 2 d System.out.println(ans) System.out.println System.out System System.out ans public class Main {

    public static void main(String[] args) {
        solve();
    }

    private static void solve() {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int d = input.nextInt();

        int ans = 0;

        while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        }

        System.out.println(ans);

    }
} public class Main {

    public static void main(String[] args) {
        solve();
    }

    private static void solve() {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int d = input.nextInt();

        int ans = 0;

        while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        }

        System.out.println(ans);

    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        solve();
    }

    private static void solve() {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int d = input.nextInt();

        int ans = 0;

        while(n > 0) {
        	ans++;
        	n = n - 1 - 2*d;
        }

        System.out.println(ans);

    }
}
