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 now = D*2+1;
		int count =1;
		while(N>now) {
			now +=D*2+1;
			count++;
		}
		System.out.println(count);
	}
} 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 now = D*2+1;
		int count =1;
		while(N>now) {
			now +=D*2+1;
			count++;
		}
		System.out.println(count);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int now = D*2+1;
		int count =1;
		while(N>now) {
			now +=D*2+1;
			count++;
		}
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int now = D*2+1;
		int count =1;
		while(N>now) {
			now +=D*2+1;
			count++;
		}
		System.out.println(count);
	} 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 now = D*2+1; now D*2+1 D*2 D 2 1 int count =1; count 1 while(N>now) {
			now +=D*2+1;
			count++;
		} N>now N now {
			now +=D*2+1;
			count++;
		} now +=D*2+1 now D*2+1 D*2 D 2 1 count++ count System.out.println(count) System.out.println System.out System System.out count 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 now = D*2+1;
		int count =1;
		while(N>now) {
			now +=D*2+1;
			count++;
		}
		System.out.println(count);
	}
} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int now = D*2+1;
		int count =1;
		while(N>now) {
			now +=D*2+1;
			count++;
		}
		System.out.println(count);
	}
} 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 now = D*2+1;
		int count =1;
		while(N>now) {
			now +=D*2+1;
			count++;
		}
		System.out.println(count);
	}
}
