import java.util.*;


public class Main {

    private static final int INF = 1000000007;
    private static final int INF1 = Integer.MAX_VALUE;

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

    private static final int INF = 1000000007;
    private static final int INF1 = Integer.MAX_VALUE;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int a = n / (2*d + 1);
        int mod = n % (2*d + 1);
        if(mod != 0){
            a += 1;
        }
        System.out.println(a);
    }
} Main private static final int INF = 1000000007; INF 1000000007 private static final int INF1 = Integer.MAX_VALUE; INF1 Integer.MAX_VALUE Integer Integer.MAX_VALUE public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int a = n / (2*d + 1);
        int mod = n % (2*d + 1);
        if(mod != 0){
            a += 1;
        }
        System.out.println(a);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int a = n / (2*d + 1);
        int mod = n % (2*d + 1);
        if(mod != 0){
            a += 1;
        }
        System.out.println(a);
    } 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 a = n / (2*d + 1); a n / (2*d + 1) n (2*d + 1) 2*d 2 d 1 int mod = n % (2*d + 1); mod n % (2*d + 1) n (2*d + 1) 2*d 2 d 1 if(mod != 0){
            a += 1;
        } mod != 0 mod 0 {
            a += 1;
        } a += 1 a 1 System.out.println(a) System.out.println System.out System System.out a String[] args args public class Main {

    private static final int INF = 1000000007;
    private static final int INF1 = Integer.MAX_VALUE;

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

    private static final int INF = 1000000007;
    private static final int INF1 = Integer.MAX_VALUE;

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


public class Main {

    private static final int INF = 1000000007;
    private static final int INF1 = Integer.MAX_VALUE;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int a = n / (2*d + 1);
        int mod = n % (2*d + 1);
        if(mod != 0){
            a += 1;
        }
        System.out.println(a);
    }
}
