output_description: Print the minimum number of inspectors that we need to deploy to achieve the
  objective.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N D
attempt: import io
  import sys
  from math import ceil
  
  
  def IN_S():
      return input()
  
  
  def IN_I():
      return int(input())
  
  
  def IN_L_I():
      return list(map(int, input().split()))
  
  
  def IN_L_S():
      return list(map(str, input().split()))
  
  
  def STR_SPLIT(s, n):
      for l in range(0, len(s), n):
          yield s[0 + l : n + l]
  
  
  def T_IN():
      global test_str
      sys.stdin = io.StringIO(test_str[1:-1])
  
  
  test_str = """
  20 4
  """
  
  
  def MAIN():
      T_IN()
      A()
  
  
  def A():
      n, d = IN_L_I()
  
      print(ceil(n / (d * 2 + 1)))
  
      return None
  
  
  def B():
      return None
  
  
  def C():
      return None
  
  
  MAIN()
  
problem_description: Statement
  
  There are N apple trees in a row. People say that one of them will bear golden
  apples.
  
  We want to deploy some number of inspectors so that each of these trees will
  be inspected.
  
  Each inspector will be deployed under one of the trees. For convenience, we
  will assign numbers from 1 through N to the trees. An inspector deployed under
  the i-th tree (1 \leq i \leq N) will inspect the trees with numbers between
  i-D and i+D (inclusive).
  
  Find the minimum number of inspectors that we need to deploy to achieve the
  objective.
samples: [{"input": "6 2", "output": "2\n    \n\nWe can achieve the objective by, for example, placing an inspector under Tree\n3 and Tree 4.\n\n* * *"}, {"input": "14 3", "output": "2\n    \n\n* * *"}, {"input": "20 4", "output": "3"}]