import java.util.*;

public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;
        ans = (n + (d * 2 + 1) -1) / (d * 2 + 1);
        System.out.println(ans);
    }
} import java.util.*; util.* java public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;
        ans = (n + (d * 2 + 1) -1) / (d * 2 + 1);
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;
        ans = (n + (d * 2 + 1) -1) / (d * 2 + 1);
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;
        ans = (n + (d * 2 + 1) -1) / (d * 2 + 1);
        System.out.println(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 ans = 0; ans 0 ans = (n + (d * 2 + 1) -1) / (d * 2 + 1) ans (n + (d * 2 + 1) -1) / (d * 2 + 1) (n + (d * 2 + 1) -1) n + (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 1 (d * 2 + 1) d * 2 d 2 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;
        ans = (n + (d * 2 + 1) -1) / (d * 2 + 1);
        System.out.println(ans);
    }
} public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;
        ans = (n + (d * 2 + 1) -1) / (d * 2 + 1);
        System.out.println(ans);
    }
} Main
import java.util.*;

public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;
        ans = (n + (d * 2 + 1) -1) / (d * 2 + 1);
        System.out.println(ans);
    }
}