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() * 2 + 1;
		int ans =0;
		ans = N/D;
		if (N%D > 0) {ans++;}

		System.out.println(ans);

	}
} 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() * 2 + 1;
		int ans =0;
		ans = N/D;
		if (N%D > 0) {ans++;}

		System.out.println(ans);

	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt() * 2 + 1;
		int ans =0;
		ans = N/D;
		if (N%D > 0) {ans++;}

		System.out.println(ans);

	} main {
		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt() * 2 + 1;
		int ans =0;
		ans = N/D;
		if (N%D > 0) {ans++;}

		System.out.println(ans);

	} 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() * 2 + 1; D sc.nextInt() * 2 + 1 sc.nextInt() * 2 sc.nextInt() sc.nextInt sc 2 1 int ans =0; ans 0 ans = N/D ans N/D N D if (N%D > 0) {ans++;} N%D > 0 N%D N D 0 {ans++;} ans++ ans System.out.println(ans) System.out.println System.out System System.out ans 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() * 2 + 1;
		int ans =0;
		ans = N/D;
		if (N%D > 0) {ans++;}

		System.out.println(ans);

	}
} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt() * 2 + 1;
		int ans =0;
		ans = N/D;
		if (N%D > 0) {ans++;}

		System.out.println(ans);

	}
} 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() * 2 + 1;
		int ans =0;
		ans = N/D;
		if (N%D > 0) {ans++;}

		System.out.println(ans);

	}
}
