output_description: Print the minimum number of elements that needs to be removed so that a will
  be a good sequence.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      a_1 a_2 ... a_N
attempt: n = int(input())
  arr = list(map(int, input().split()))
  t = 0
  for i in set(arr):
      t += i
  print(abs(n - t))
  
problem_description: Statement
  
  You are given a sequence of positive integers of length N, a = (a_1, a_2, ...,
  a_N). Your objective is to remove some of the elements in a so that a will be
  a **good sequence**.
  
  Here, an sequence b is a **good sequence** when the following condition holds
  true:
  
    * For each element x in b, the value x occurs exactly x times in b.
  
  For example, (3, 3, 3), (4, 2, 4, 1, 4, 2, 4) and () (an empty sequence) are
  good sequences, while (3, 3, 3, 3) and (2, 4, 1, 4, 2) are not.
  
  Find the minimum number of elements that needs to be removed so that a will be
  a good sequence.
samples: [{"input": "4\n    3 3 3 3", "output": "1\n    \n\nWe can, for example, remove one occurrence of 3. Then, (3, 3, 3) is a good\nsequence.\n\n* * *"}, {"input": "5\n    2 4 1 4 2", "output": "2\n    \n\nWe can, for example, remove two occurrences of 4. Then, (2, 1, 2) is a good\nsequence.\n\n* * *"}, {"input": "6\n    1 2 2 3 3 3", "output": "0\n    \n\n* * *"}, {"input": "1\n    1000000000", "output": "1\n    \n\nRemove one occurrence of 10^9. Then, () is a good sequence.\n\n* * *"}, {"input": "8\n    2 7 1 8 2 8 1 8", "output": "5"}]