import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  }
}

/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