import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		final int N = Integer.parseInt(sc.next());
		final int D = Integer.parseInt(sc.next());

		BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0));
		ans =  ans.setScale(0, RoundingMode.CEILING);
		System.out.println(ans);


	}

} import java.math.BigDecimal; BigDecimal java.math import java.math.RoundingMode; RoundingMode java.math import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		final int N = Integer.parseInt(sc.next());
		final int D = Integer.parseInt(sc.next());

		BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0));
		ans =  ans.setScale(0, RoundingMode.CEILING);
		System.out.println(ans);


	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		final int N = Integer.parseInt(sc.next());
		final int D = Integer.parseInt(sc.next());

		BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0));
		ans =  ans.setScale(0, RoundingMode.CEILING);
		System.out.println(ans);


	} main {
		Scanner sc = new Scanner(System.in);
		final int N = Integer.parseInt(sc.next());
		final int D = Integer.parseInt(sc.next());

		BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0));
		ans =  ans.setScale(0, RoundingMode.CEILING);
		System.out.println(ans);


	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc final int D = Integer.parseInt(sc.next()); D Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0)); ans BigDecimal.valueOf(N / (D * 2 + 1.0)) BigDecimal.valueOf BigDecimal N / (D * 2 + 1.0) N (D * 2 + 1.0) D * 2 D 2 1.0 ans =  ans.setScale(0, RoundingMode.CEILING) ans ans.setScale(0, RoundingMode.CEILING) ans.setScale ans 0 RoundingMode.CEILING RoundingMode RoundingMode.CEILING 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);
		final int N = Integer.parseInt(sc.next());
		final int D = Integer.parseInt(sc.next());

		BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0));
		ans =  ans.setScale(0, RoundingMode.CEILING);
		System.out.println(ans);


	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		final int N = Integer.parseInt(sc.next());
		final int D = Integer.parseInt(sc.next());

		BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0));
		ans =  ans.setScale(0, RoundingMode.CEILING);
		System.out.println(ans);


	}

} Main
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		final int N = Integer.parseInt(sc.next());
		final int D = Integer.parseInt(sc.next());

		BigDecimal ans = BigDecimal.valueOf(N / (D * 2 + 1.0));
		ans =  ans.setScale(0, RoundingMode.CEILING);
		System.out.println(ans);


	}

}
