output_description: Print the maximum number of pairs that can be created.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      N M
      X_1 X_2 ... X_N
attempt: from collections import Counter as c
  
  n, m = map(int, input().split())
  a = list(map(int, input().split()))
  b = c(a)
  d = [0] * m
  e = [0] * m
  for i in b.keys():
      t = b[i]
      d[i % m] += t
      e[i % m] += t // 2
  z = 0
  for i in range(1, m // 2):
      x, y = d[i], d[-i]
      if x > y:
          z += d[-i] + min(e[i], (d[i] - d[-i]) // 2)
      else:
          z += d[i] + min(e[-i], (d[-i] - d[i]) // 2)
  if m % 2 == 0:
      z += d[m // 2] // 2
  z += d[0] // 2
  print(z)
  
problem_description: Statement
  
  Takahashi is playing with N cards.
  
  The i-th card has an integer X_i on it.
  
  Takahashi is trying to create as many pairs of cards as possible satisfying
  one of the following conditions:
  
    * The integers on the two cards are the same.
    * The sum of the integers on the two cards is a multiple of M.
  
  Find the maximum number of pairs that can be created.
  
  Note that a card cannot be used in more than one pair.
samples: [{"input": "7 5\n    3 1 4 1 5 9 2", "output": "3\n    \n\nThree pairs (3,2), (1,4) and (1,9) can be created.\n\nIt is possible to create pairs (3,2) and (1,1), but the number of pairs is not\nmaximized with this.\n\n* * *"}, {"input": "15 10\n    1 5 6 10 11 11 11 20 21 25 25 26 99 99 99", "output": "6"}]