import java.util.*;

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

        int appleNum = sc.nextInt();
        int sight = sc.nextInt() * 2 + 1;

        int ans = (int)Math.ceil((double)appleNum / (double)sight);

        System.out.println(ans);
    }
} import java.util.*; util.* java class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int appleNum = sc.nextInt();
        int sight = sc.nextInt() * 2 + 1;

        int ans = (int)Math.ceil((double)appleNum / (double)sight);

        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int appleNum = sc.nextInt();
        int sight = sc.nextInt() * 2 + 1;

        int ans = (int)Math.ceil((double)appleNum / (double)sight);

        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);

        int appleNum = sc.nextInt();
        int sight = sc.nextInt() * 2 + 1;

        int ans = (int)Math.ceil((double)appleNum / (double)sight);

        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int appleNum = sc.nextInt(); appleNum sc.nextInt() sc.nextInt sc int sight = sc.nextInt() * 2 + 1; sight sc.nextInt() * 2 + 1 sc.nextInt() * 2 sc.nextInt() sc.nextInt sc 2 1 int ans = (int)Math.ceil((double)appleNum / (double)sight); ans (int)Math.ceil((double)appleNum / (double)sight) Math.ceil Math (double)appleNum / (double)sight (double)appleNum (double)sight System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;

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

        int appleNum = sc.nextInt();
        int sight = sc.nextInt() * 2 + 1;

        int ans = (int)Math.ceil((double)appleNum / (double)sight);

        System.out.println(ans);
    }
}