output_description: Print the total horizontal length of the uncovered parts of the window.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      A B
attempt: # cook your dish here
  import sys
  
  
  def file():
      sys.stdin = open("input.py", "r")
      sys.stdout = open("output.py", "w")
  
  
  # file()
  def main(N, arr):
  
      # initialising with positive infinity value
      maxi = float("inf")
  
      # initialising the answer variable
      ans = 0
  
      # iterating linesrly
      for i in range(N):
  
          # finding minimum at each step
          maxi = min(maxi, arr[i])
          # increasing the final ans
          ans += maxi
          print("dhh")
  
      # returning the answer
      return ans
  
  
  if __name__ == "__main__":
  
      # length of the array
      """N = 4
  
      #Maximum size of each individual bucket
      Arr = [4,3,2,1]
  
      #passing the values to the main function
      answer = main(N,Arr)
  
      #printing the result
      print(answer)"""
  
      a, b = map(int, input().split())
      d = a - (2 * b)
      if d < 0:
          print(0)
      else:
          print(d)
  
problem_description: Statement
  
  The window of Takahashi's room has a width of A. There are two curtains hung
  over the window, each of which has a horizontal length of B. (Vertically, the
  curtains are long enough to cover the whole window.)
  
  We will close the window so as to minimize the total horizontal length of the
  uncovered part of the window. Find the total horizontal length of the
  uncovered parts of the window then.
samples: [{"input": "12 4", "output": "4\n    \n\nWe have a window with a horizontal length of 12, and two curtains, each of\nlength 4, that cover both ends of the window, for example. The uncovered part\nhas a horizontal length of 4.\n\n* * *"}, {"input": "20 15", "output": "0\n    \n\nIf the window is completely covered, print 0.\n\n* * *"}, {"input": "20 30", "output": "0\n    \n\nEach curtain may be longer than the window."}]