import java.util.Scanner;

class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count=0;
		for(int i=1;i<=n;i+=d*2+1)count++;
		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count=0;
		for(int i=1;i<=n;i+=d*2+1)count++;
		System.out.println(count);
	}
} Main public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count=0;
		for(int i=1;i<=n;i+=d*2+1)count++;
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count=0;
		for(int i=1;i<=n;i+=d*2+1)count++;
		System.out.println(count);
	} 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 count=0; count 0 for(int i=1;i<=n;i+=d*2+1)count++; int i=1; int i=1; i 1 i<=n i n i+=d*2+1 i+=d*2+1 i d*2+1 d*2 d 2 1 count++; count++ count System.out.println(count) System.out.println System.out System System.out count String args[] args
import java.util.Scanner;

class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count=0;
		for(int i=1;i<=n;i+=d*2+1)count++;
		System.out.println(count);
	}
}
