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: # cook your dish here
  import numpy as np
  
  if __name__ == "__main__":
      xy = [int(i) for i in input().split()]
      a1 = np.array([xy[0], xy[1]])
      a2 = np.array([xy[2], xy[3]])
      b = a2 - a1
      r = np.pi / 2
      rot = np.matrix(((np.cos(r), np.sin(r)), (-np.sin(r), np.cos(r))))
      c = np.dot(b, rot)
      a3 = a2 + c
      a4 = a1 + c
      print(
          "{} {} {} {}".format(
              np.round(a3[0, 0]),
              np.round(a3[0, 1]),
              np.round(a4[0, 0]),
              np.round(a4[0, 1]),
          )
      )
  
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"}]