import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);


		int trees = scan.nextInt();
		int canSee =scan.nextInt()*2+1;

		int needMen=0;
		for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		}



		System.out.println(needMen);

	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);


		int trees = scan.nextInt();
		int canSee =scan.nextInt()*2+1;

		int needMen=0;
		for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		}



		System.out.println(needMen);

	}
} Main public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);


		int trees = scan.nextInt();
		int canSee =scan.nextInt()*2+1;

		int needMen=0;
		for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		}



		System.out.println(needMen);

	} main {

		Scanner scan = new Scanner(System.in);


		int trees = scan.nextInt();
		int canSee =scan.nextInt()*2+1;

		int needMen=0;
		for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		}



		System.out.println(needMen);

	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int trees = scan.nextInt(); trees scan.nextInt() scan.nextInt scan int canSee =scan.nextInt()*2+1; canSee scan.nextInt()*2+1 scan.nextInt()*2 scan.nextInt() scan.nextInt scan 2 1 int needMen=0; needMen 0 for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		} ; trees>0 trees 0 {

			trees=trees-canSee;
			needMen++;
		} {

			trees=trees-canSee;
			needMen++;
		} trees=trees-canSee trees trees-canSee trees canSee needMen++ needMen System.out.println(needMen) System.out.println System.out System System.out needMen String[] args args public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);


		int trees = scan.nextInt();
		int canSee =scan.nextInt()*2+1;

		int needMen=0;
		for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		}



		System.out.println(needMen);

	}
} public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);


		int trees = scan.nextInt();
		int canSee =scan.nextInt()*2+1;

		int needMen=0;
		for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		}



		System.out.println(needMen);

	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);


		int trees = scan.nextInt();
		int canSee =scan.nextInt()*2+1;

		int needMen=0;
		for(;trees>0;) {

			trees=trees-canSee;
			needMen++;
		}



		System.out.println(needMen);

	}
}
