import java.util.*;
import java.io.*;
import java.lang.*;
import java.math.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner (System.in);
		double n = sc.nextInt();
		double d = sc.nextInt() * 2 + 1;
		sc.close();
		double ans = Math.ceil(n/d);
		System.out.println((int)ans);
	}
} import java.util.*; util.* java import java.io.*; io.* java import java.lang.*; lang.* java import java.math.*; math.* java public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner (System.in);
		double n = sc.nextInt();
		double d = sc.nextInt() * 2 + 1;
		sc.close();
		double ans = Math.ceil(n/d);
		System.out.println((int)ans);
	}
} Main public static void main (String[] args) {
		Scanner sc = new Scanner (System.in);
		double n = sc.nextInt();
		double d = sc.nextInt() * 2 + 1;
		sc.close();
		double ans = Math.ceil(n/d);
		System.out.println((int)ans);
	} main {
		Scanner sc = new Scanner (System.in);
		double n = sc.nextInt();
		double d = sc.nextInt() * 2 + 1;
		sc.close();
		double ans = Math.ceil(n/d);
		System.out.println((int)ans);
	} Scanner sc = new Scanner (System.in); sc new Scanner (System.in) double n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double d = sc.nextInt() * 2 + 1; d sc.nextInt() * 2 + 1 sc.nextInt() * 2 sc.nextInt() sc.nextInt sc 2 1 sc.close() sc.close sc double ans = Math.ceil(n/d); ans Math.ceil(n/d) Math.ceil Math n/d n d System.out.println((int)ans) System.out.println System.out System System.out (int)ans String[] args args public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner (System.in);
		double n = sc.nextInt();
		double d = sc.nextInt() * 2 + 1;
		sc.close();
		double ans = Math.ceil(n/d);
		System.out.println((int)ans);
	}
} public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner (System.in);
		double n = sc.nextInt();
		double d = sc.nextInt() * 2 + 1;
		sc.close();
		double ans = Math.ceil(n/d);
		System.out.println((int)ans);
	}
} Main
import java.util.*;
import java.io.*;
import java.lang.*;
import java.math.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner (System.in);
		double n = sc.nextInt();
		double d = sc.nextInt() * 2 + 1;
		sc.close();
		double ans = Math.ceil(n/d);
		System.out.println((int)ans);
	}
}
