import java.util.Scanner;

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

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