output_description: Print the answer.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: N = input()
  if (int(N) % 2) == 0:
      print(int(int(N) / 2))
  else:
      print(int((int(N) - 1) / 2))
  
problem_description: Statement
  
  How many ways are there to choose two distinct positive integers totaling N,
  disregarding the order?
samples: [{"input": "4", "output": "1\n    \n\nThere is only one way to choose two distinct integers totaling 4: to choose 1\nand 3. (Choosing 3 and 1 is not considered different from this.)\n\n* * *"}, {"input": "999999", "output": "499999"}]