import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int n = scan.nextInt();
		int d = scan.nextInt();
		int can = 2*d+1;
		int ans = 0;
		if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		}
		System.out.println(ans);
	}

}


 import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int n = scan.nextInt();
		int d = scan.nextInt();
		int can = 2*d+1;
		int ans = 0;
		if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		}
		System.out.println(ans);
	}

} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int n = scan.nextInt();
		int d = scan.nextInt();
		int can = 2*d+1;
		int ans = 0;
		if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		}
		System.out.println(ans);
	} main {
		Scanner scan = new Scanner(System.in);
		
		int n = scan.nextInt();
		int d = scan.nextInt();
		int can = 2*d+1;
		int ans = 0;
		if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		}
		System.out.println(ans);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int d = scan.nextInt(); d scan.nextInt() scan.nextInt scan int can = 2*d+1; can 2*d+1 2*d 2 d 1 int ans = 0; ans 0 if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		} n%can == 0 n%can n can 0 {
			ans = n/can;
		} ans = n/can ans n/can n can {
			ans = n/can+1;
		} ans = n/can+1 ans n/can+1 n/can n can 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 scan = new Scanner(System.in);
		
		int n = scan.nextInt();
		int d = scan.nextInt();
		int can = 2*d+1;
		int ans = 0;
		if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		}
		System.out.println(ans);
	}

} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int n = scan.nextInt();
		int d = scan.nextInt();
		int can = 2*d+1;
		int ans = 0;
		if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		}
		System.out.println(ans);
	}

} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int n = scan.nextInt();
		int d = scan.nextInt();
		int can = 2*d+1;
		int ans = 0;
		if(n%can == 0) {
			ans = n/can;
		}else {
			ans = n/can+1;
		}
		System.out.println(ans);
	}

}



