
import java.util.Scanner;

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

        int N = scanner.nextInt();
        int D = scanner.nextInt();
        
        int answer = N / (2 * D + 1);
        if (N % (2 * D + 1) > 0) {
            answer++;
        }

        System.out.println(answer);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();
        int D = scanner.nextInt();
        
        int answer = N / (2 * D + 1);
        if (N % (2 * D + 1) > 0) {
            answer++;
        }

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

        int N = scanner.nextInt();
        int D = scanner.nextInt();
        
        int answer = N / (2 * D + 1);
        if (N % (2 * D + 1) > 0) {
            answer++;
        }

        System.out.println(answer);
    } main {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();
        int D = scanner.nextInt();
        
        int answer = N / (2 * D + 1);
        if (N % (2 * D + 1) > 0) {
            answer++;
        }

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

        int N = scanner.nextInt();
        int D = scanner.nextInt();
        
        int answer = N / (2 * D + 1);
        if (N % (2 * D + 1) > 0) {
            answer++;
        }

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

        int N = scanner.nextInt();
        int D = scanner.nextInt();
        
        int answer = N / (2 * D + 1);
        if (N % (2 * D + 1) > 0) {
            answer++;
        }

        System.out.println(answer);
    }
} Main

import java.util.Scanner;

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

        int N = scanner.nextInt();
        int D = scanner.nextInt();
        
        int answer = N / (2 * D + 1);
        if (N % (2 * D + 1) > 0) {
            answer++;
        }

        System.out.println(answer);
    }
}
