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 ninzuu = 0;
		
		D = D*2+1;
		do {
			N = N-D;
			ninzuu++;
		} while (N > 0);
		
		System.out.println(ninzuu);
		
		sc.close();
	}
} 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 ninzuu = 0;
		
		D = D*2+1;
		do {
			N = N-D;
			ninzuu++;
		} while (N > 0);
		
		System.out.println(ninzuu);
		
		sc.close();
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int ninzuu = 0;
		
		D = D*2+1;
		do {
			N = N-D;
			ninzuu++;
		} while (N > 0);
		
		System.out.println(ninzuu);
		
		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int ninzuu = 0;
		
		D = D*2+1;
		do {
			N = N-D;
			ninzuu++;
		} while (N > 0);
		
		System.out.println(ninzuu);
		
		sc.close();
	} 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 ninzuu = 0; ninzuu 0 D = D*2+1 D D*2+1 D*2 D 2 1 do {
			N = N-D;
			ninzuu++;
		} while (N > 0); N > 0 N 0 {
			N = N-D;
			ninzuu++;
		} N = N-D N N-D N D ninzuu++ ninzuu System.out.println(ninzuu) System.out.println System.out System System.out ninzuu sc.close() sc.close sc 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 ninzuu = 0;
		
		D = D*2+1;
		do {
			N = N-D;
			ninzuu++;
		} while (N > 0);
		
		System.out.println(ninzuu);
		
		sc.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int ninzuu = 0;
		
		D = D*2+1;
		do {
			N = N-D;
			ninzuu++;
		} while (N > 0);
		
		System.out.println(ninzuu);
		
		sc.close();
	}
} 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 ninzuu = 0;
		
		D = D*2+1;
		do {
			N = N-D;
			ninzuu++;
		} while (N > 0);
		
		System.out.println(ninzuu);
		
		sc.close();
	}
}