import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt(), D = in.nextInt() * 2 + 1;
        System.out.println(N / D + (N % D == 0 ? 0 : 1));
    }
} import java.util.*; util.* java import java.util.stream.*; stream.* java.util public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt(), D = in.nextInt() * 2 + 1;
        System.out.println(N / D + (N % D == 0 ? 0 : 1));
    }
} Main public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt(), D = in.nextInt() * 2 + 1;
        System.out.println(N / D + (N % D == 0 ? 0 : 1));
    } main {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt(), D = in.nextInt() * 2 + 1;
        System.out.println(N / D + (N % D == 0 ? 0 : 1));
    } Scanner in = new Scanner(System.in); in new Scanner(System.in) int N = in.nextInt() N in.nextInt() in.nextInt in D = in.nextInt() * 2 + 1; D in.nextInt() * 2 + 1 in.nextInt() * 2 in.nextInt() in.nextInt in 2 1 System.out.println(N / D + (N % D == 0 ? 0 : 1)) System.out.println System.out System System.out N / D + (N % D == 0 ? 0 : 1) N / D N D (N % D == 0 ? 0 : 1) N % D == 0 N % D N D 0 0 1 String[] args args public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt(), D = in.nextInt() * 2 + 1;
        System.out.println(N / D + (N % D == 0 ? 0 : 1));
    }
} public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt(), D = in.nextInt() * 2 + 1;
        System.out.println(N / D + (N % D == 0 ? 0 : 1));
    }
} Main
import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt(), D = in.nextInt() * 2 + 1;
        System.out.println(N / D + (N % D == 0 ? 0 : 1));
    }
}