
import 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 count=0;
		
		for(int i=0;i<N;i+=D*2+1) {
			count++;
		}
		System.out.println(count);
		sc.close();
	}
} import java.util.*; util.* java public 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=0;i<N;i+=D*2+1) {
			count++;
		}
		System.out.println(count);
		sc.close();
	}
} 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=0;i<N;i+=D*2+1) {
			count++;
		}
		System.out.println(count);
		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int count=0;
		
		for(int i=0;i<N;i+=D*2+1) {
			count++;
		}
		System.out.println(count);
		sc.close();
	} 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=0;i<N;i+=D*2+1) {
			count++;
		} int i=0; int i=0; i 0 i<N i N i+=D*2+1 i+=D*2+1 i D*2+1 D*2 D 2 1 {
			count++;
		} {
			count++;
		} count++ count System.out.println(count) System.out.println System.out System System.out count sc.close() sc.close sc 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 count=0;
		
		for(int i=0;i<N;i+=D*2+1) {
			count++;
		}
		System.out.println(count);
		sc.close();
	}
} public 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=0;i<N;i+=D*2+1) {
			count++;
		}
		System.out.println(count);
		sc.close();
	}
} Main

import 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 count=0;
		
		for(int i=0;i<N;i+=D*2+1) {
			count++;
		}
		System.out.println(count);
		sc.close();
	}
}
