import java.util.*;
import static java.lang.Math.*;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		// 入力
		double n = sc.nextInt();
		double d = sc.nextInt();
		
		// 計算
		int result = (int)ceil(n/(2*d + 1));
		
		// 出力
		System.out.println(result);
	}

} import java.util.*; util.* java import static java.lang.Math.*; import static java.lang.Math.*; import static java.lang.Math.*; import java.math.BigInteger; BigInteger java.math public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		// 入力
		double n = sc.nextInt();
		double d = sc.nextInt();
		
		// 計算
		int result = (int)ceil(n/(2*d + 1));
		
		// 出力
		System.out.println(result);
	}

} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		// 入力
		double n = sc.nextInt();
		double d = sc.nextInt();
		
		// 計算
		int result = (int)ceil(n/(2*d + 1));
		
		// 出力
		System.out.println(result);
	} main {
		Scanner sc = new Scanner(System.in);

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

		// 入力
		double n = sc.nextInt();
		double d = sc.nextInt();
		
		// 計算
		int result = (int)ceil(n/(2*d + 1));
		
		// 出力
		System.out.println(result);
	}

} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		// 入力
		double n = sc.nextInt();
		double d = sc.nextInt();
		
		// 計算
		int result = (int)ceil(n/(2*d + 1));
		
		// 出力
		System.out.println(result);
	}

} Main
import java.util.*;
import static java.lang.Math.*;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		// 入力
		double n = sc.nextInt();
		double d = sc.nextInt();
		
		// 計算
		int result = (int)ceil(n/(2*d + 1));
		
		// 出力
		System.out.println(result);
	}

}
