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