import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    }

}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz