//ｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｹｰｰｰｰｯ!!!wwwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwwｺｹｯwwwｺｹｯｺｯwwwｺｹｰｰｰｰｯ!!!wwwwwｺｹｯｺｯｯｺｰｰｰｰ!!!!!!wwwwwwwwwww
import java.util.*;
public class Main {
    public static void main(final String[] args) {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    }
} import java.util.*; util.* java public class Main {
    public static void main(final String[] args) {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    }
} Main public static void main(final String[] args) {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    } main {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    } final Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc final int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc sc.close() sc.close sc int yono = n / (d * 2 + 1); yono n / (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 if(n % (2 * d + 1) != 0) yono++; n % (2 * d + 1) != 0 n % (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 0 yono++ yono System.out.println(yono) System.out.println System.out System System.out yono final String[] args args public class Main {
    public static void main(final String[] args) {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    }
} public class Main {
    public static void main(final String[] args) {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    }
} Main
//ｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｹｰｰｰｰｯ!!!wwwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwwｺｹｯwwwｺｹｯｺｯwwwｺｹｰｰｰｰｯ!!!wwwwwｺｹｯｺｯｯｺｰｰｰｰ!!!!!!wwwwwwwwwww
import java.util.*;
public class Main {
    public static void main(final String[] args) {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    }
}