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: N, D = map(int, input())
  if N % 2 * D + 1 == 0:
      print(N // ((2 * D) + 1))
  else:
      print(N // ((2 * D) + 1) + 1)
  
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"}]