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 ans;

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

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

		if(N%(D+1+D)>0) {
			ans = N / (D + 1 + D)+1;
		} else {
			ans = N / (D + 1 + D);
		}
		System.out.println(ans);
     } main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int ans;

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

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

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

		if(N%(D+1+D)>0) {
			ans = N / (D + 1 + D)+1;
		} else {
			ans = N / (D + 1 + D);
		}
		System.out.println(ans);
     }

	}
