import java.util.*;
import static java.lang.Integer.*;
//import static java.lang.Long.*;
import static java.lang.Math.*;
import static java.lang.System.*;

public class Main {
	public static void main(String[] args) {
		int i,j,k;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int d = parseInt(sc.next());
		sc.close();
		out.println((int)ceil((double)n/(2*d+1)));
	}
} import java.util.*; util.* java import static java.lang.Integer.*; import static java.lang.Integer.*; import static java.lang.Integer.*; import static java.lang.Math.*; import static java.lang.Math.*; import static java.lang.Math.*; import static java.lang.System.*; import static java.lang.System.*; import static java.lang.System.*; public class Main {
	public static void main(String[] args) {
		int i,j,k;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int d = parseInt(sc.next());
		sc.close();
		out.println((int)ceil((double)n/(2*d+1)));
	}
} Main public static void main(String[] args) {
		int i,j,k;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int d = parseInt(sc.next());
		sc.close();
		out.println((int)ceil((double)n/(2*d+1)));
	} main {
		int i,j,k;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int d = parseInt(sc.next());
		sc.close();
		out.println((int)ceil((double)n/(2*d+1)));
	} int i i j j k; k Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = parseInt(sc.next()); n parseInt(sc.next()) parseInt sc.next() sc.next sc int d = parseInt(sc.next()); d parseInt(sc.next()) parseInt sc.next() sc.next sc sc.close() sc.close sc out.println((int)ceil((double)n/(2*d+1))) out.println out (int)ceil((double)n/(2*d+1)) ceil (double)n/(2*d+1) (double)n (2*d+1) 2*d 2 d 1 String[] args args public class Main {
	public static void main(String[] args) {
		int i,j,k;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int d = parseInt(sc.next());
		sc.close();
		out.println((int)ceil((double)n/(2*d+1)));
	}
} public class Main {
	public static void main(String[] args) {
		int i,j,k;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int d = parseInt(sc.next());
		sc.close();
		out.println((int)ceil((double)n/(2*d+1)));
	}
} Main
import java.util.*;
import static java.lang.Integer.*;
//import static java.lang.Long.*;
import static java.lang.Math.*;
import static java.lang.System.*;

public class Main {
	public static void main(String[] args) {
		int i,j,k;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int d = parseInt(sc.next());
		sc.close();
		out.println((int)ceil((double)n/(2*d+1)));
	}
}
