//package atcoder;

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 = 1;
			int A = (2*D+1)*1;
		while(A<N) {
			count ++;
			A = (2*D+1)*count;
			
		}
		
		System.out.println(count);
	}		
} 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 = 1;
			int A = (2*D+1)*1;
		while(A<N) {
			count ++;
			A = (2*D+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 = 1;
			int A = (2*D+1)*1;
		while(A<N) {
			count ++;
			A = (2*D+1)*count;
			
		}
		
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
			int N= sc.nextInt();	
			int D = sc.nextInt();
			
	
			int count = 1;
			int A = (2*D+1)*1;
		while(A<N) {
			count ++;
			A = (2*D+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 = 1; count 1 int A = (2*D+1)*1; A (2*D+1)*1 (2*D+1) 2*D 2 D 1 1 while(A<N) {
			count ++;
			A = (2*D+1)*count;
			
		} A<N A N {
			count ++;
			A = (2*D+1)*count;
			
		} count ++ count A = (2*D+1)*count A (2*D+1)*count (2*D+1) 2*D 2 D 1 count System.out.println(count) System.out.println System.out System System.out count 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 = 1;
			int A = (2*D+1)*1;
		while(A<N) {
			count ++;
			A = (2*D+1)*count;
			
		}
		
		System.out.println(count);
	}		
} 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 = 1;
			int A = (2*D+1)*1;
		while(A<N) {
			count ++;
			A = (2*D+1)*count;
			
		}
		
		System.out.println(count);
	}		
} Main
//package atcoder;

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 = 1;
			int A = (2*D+1)*1;
		while(A<N) {
			count ++;
			A = (2*D+1)*count;
			
		}
		
		System.out.println(count);
	}		
}