output_description: Print the number of ways to choose a pair of an even number and an odd number
  from the positive integers between 1 and K (inclusive).
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      K
attempt: import math
  
  
  def li():
      return list(map(int, input().split()))
  
  
  def mi():
      return map(int, input().split())
  
  
  def ii():
      return int(input())
  
  
  x1, y1, x2, y2 = mi()
  
  l = 0
  # x = Cの場合
  if (x2 - x1) == 0:
      l = y2 - y1
      if y2 > y1:
          x3 = x1 - l
      else:
          x3 = x1 + l
      y3 = y2
      x4 = x3
      y4 = y1
  # y = Cの場合
  elif (y2 - y1) == 0:
      l = x2 - x1
      x3 = x2
      if x2 > x1:
          y3 = y2 - l
      else:
          y3 = y2 + l
      x4 = x1
      y4 = y3
  # y = ax + bの場合
  else:
      x3 = x2 - (y2 - y1)
      y3 = y2 + (x2 - x1)
      x4 = x1 - (y2 - y1)
      y4 = y1 + (x2 - x1)
  
  print(x3, y3, x4, y4)
  
problem_description: Statement
  
  Find the number of ways to choose a pair of an even number and an odd number
  from the positive integers between 1 and K (inclusive). The order does not
  matter.
samples: [{"input": "3", "output": "2\n    \n\nTwo pairs can be chosen: (2,1) and (2,3).\n\n* * *"}, {"input": "6", "output": "9\n    \n\n* * *"}, {"input": "11", "output": "30\n    \n\n* * *"}, {"input": "50", "output": "625"}]