

import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);

        Double N = sc.nextDouble();
        Double D = sc.nextDouble();
        int ans = (int)Math.ceil(N / (2 * D + 1));
        System.out.println(ans);
        sc.close();
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);

        Double N = sc.nextDouble();
        Double D = sc.nextDouble();
        int ans = (int)Math.ceil(N / (2 * D + 1));
        System.out.println(ans);
        sc.close();
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);

        Double N = sc.nextDouble();
        Double D = sc.nextDouble();
        int ans = (int)Math.ceil(N / (2 * D + 1));
        System.out.println(ans);
        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);

        Double N = sc.nextDouble();
        Double D = sc.nextDouble();
        int ans = (int)Math.ceil(N / (2 * D + 1));
        System.out.println(ans);
        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) Double N = sc.nextDouble(); N sc.nextDouble() sc.nextDouble sc Double D = sc.nextDouble(); D sc.nextDouble() sc.nextDouble sc int ans = (int)Math.ceil(N / (2 * D + 1)); ans (int)Math.ceil(N / (2 * D + 1)) Math.ceil Math N / (2 * D + 1) N (2 * D + 1) 2 * D 2 D 1 System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);

        Double N = sc.nextDouble();
        Double D = sc.nextDouble();
        int ans = (int)Math.ceil(N / (2 * D + 1));
        System.out.println(ans);
        sc.close();
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);

        Double N = sc.nextDouble();
        Double D = sc.nextDouble();
        int ans = (int)Math.ceil(N / (2 * D + 1));
        System.out.println(ans);
        sc.close();
    }
} Main


import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);

        Double N = sc.nextDouble();
        Double D = sc.nextDouble();
        int ans = (int)Math.ceil(N / (2 * D + 1));
        System.out.println(ans);
        sc.close();
    }
}