import java.util.*;

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

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