import java.util.Scanner;
public class Main {

    public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
    	// 入力
    	int n = sc.nextInt();
    	int d = sc.nextInt();

    	int d2 = d + 1 + d;
    	int ans = n / d2;
    	if (n % d2 > 0){
    		ans++;
    	}


    	// 出力
    	System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
    	// 入力
    	int n = sc.nextInt();
    	int d = sc.nextInt();

    	int d2 = d + 1 + d;
    	int ans = n / d2;
    	if (n % d2 > 0){
    		ans++;
    	}


    	// 出力
    	System.out.println(ans);
    }
} Main public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
    	// 入力
    	int n = sc.nextInt();
    	int d = sc.nextInt();

    	int d2 = d + 1 + d;
    	int ans = n / d2;
    	if (n % d2 > 0){
    		ans++;
    	}


    	// 出力
    	System.out.println(ans);
    } main {
    	Scanner sc = new Scanner(System.in);
    	// 入力
    	int n = sc.nextInt();
    	int d = sc.nextInt();

    	int d2 = d + 1 + d;
    	int ans = n / d2;
    	if (n % d2 > 0){
    		ans++;
    	}


    	// 出力
    	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 d2 = d + 1 + d; d2 d + 1 + d d + 1 + d d 1 d int ans = n / d2; ans n / d2 n d2 if (n % d2 > 0){
    		ans++;
    	} n % d2 > 0 n % d2 n d2 0 {
    		ans++;
    	} ans++ ans 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);
    	// 入力
    	int n = sc.nextInt();
    	int d = sc.nextInt();

    	int d2 = d + 1 + d;
    	int ans = n / d2;
    	if (n % d2 > 0){
    		ans++;
    	}


    	// 出力
    	System.out.println(ans);
    }
} public class Main {

    public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
    	// 入力
    	int n = sc.nextInt();
    	int d = sc.nextInt();

    	int d2 = d + 1 + d;
    	int ans = n / d2;
    	if (n % d2 > 0){
    		ans++;
    	}


    	// 出力
    	System.out.println(ans);
    }
} Main
import java.util.Scanner;
public class Main {

    public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
    	// 入力
    	int n = sc.nextInt();
    	int d = sc.nextInt();

    	int d2 = d + 1 + d;
    	int ans = n / d2;
    	if (n % d2 > 0){
    		ans++;
    	}


    	// 出力
    	System.out.println(ans);
    }
}