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 Remainder = 0;
		int ans=0;
		ans=(N/((2*D)+1));
		Remainder=(N%((2*D)+1));
		if(Remainder>=1){
		ans=ans+1;
		}
		System.out.println(ans);
    }
} 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 Remainder = 0;
		int ans=0;
		ans=(N/((2*D)+1));
		Remainder=(N%((2*D)+1));
		if(Remainder>=1){
		ans=ans+1;
		}
		System.out.println(ans);
    }
} Main public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int Remainder = 0;
		int ans=0;
		ans=(N/((2*D)+1));
		Remainder=(N%((2*D)+1));
		if(Remainder>=1){
		ans=ans+1;
		}
		System.out.println(ans);
    } main {
    	Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int Remainder = 0;
		int ans=0;
		ans=(N/((2*D)+1));
		Remainder=(N%((2*D)+1));
		if(Remainder>=1){
		ans=ans+1;
		}
		System.out.println(ans);
    } 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 Remainder = 0; Remainder 0 int ans=0; ans 0 ans=(N/((2*D)+1)) ans (N/((2*D)+1)) N ((2*D)+1) (2*D) 2 D 1 Remainder=(N%((2*D)+1)) Remainder (N%((2*D)+1)) N ((2*D)+1) (2*D) 2 D 1 if(Remainder>=1){
		ans=ans+1;
		} Remainder>=1 Remainder 1 {
		ans=ans+1;
		} ans=ans+1 ans ans+1 ans 1 System.out.println(ans) System.out.println System.out System System.out ans 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 Remainder = 0;
		int ans=0;
		ans=(N/((2*D)+1));
		Remainder=(N%((2*D)+1));
		if(Remainder>=1){
		ans=ans+1;
		}
		System.out.println(ans);
    }
} public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int Remainder = 0;
		int ans=0;
		ans=(N/((2*D)+1));
		Remainder=(N%((2*D)+1));
		if(Remainder>=1){
		ans=ans+1;
		}
		System.out.println(ans);
    }
} 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 Remainder = 0;
		int ans=0;
		ans=(N/((2*D)+1));
		Remainder=(N%((2*D)+1));
		if(Remainder>=1){
		ans=ans+1;
		}
		System.out.println(ans);
    }
}