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