output_description: Print the minimum possible sadness of Snuke.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      A_1 A_2 ... A_N
attempt: n = ir()
  a = lr()
  total = 0
  for i, num in enumerate(a):
      a[i] = num - (i + 1)
  mean = sum(a) // n - 1
  ans = [0, 0, 0]
  for i in range(mean, mean + 3):
      tmp = i % 3
      for num in a:
          ans[tmp] += abs(num - i)
  print(min(ans))
  
problem_description: Statement
  
  Snuke has an integer sequence A of length N.
  
  He will freely choose an integer b. Here, he will get sad if A_i and b+i are
  far from each other. More specifically, the _sadness_ of Snuke is calculated
  as follows:
  
    * abs(A_1 - (b+1)) + abs(A_2 - (b+2)) + ... + abs(A_N - (b+N))
  
  Here, abs(x) is a function that returns the absolute value of x.
  
  Find the minimum possible sadness of Snuke.
samples: [{"input": "5\n    2 2 3 5 5", "output": "2\n    \n\nIf we choose b=0, the sadness of Snuke would be\nabs(2-(0+1))+abs(2-(0+2))+abs(3-(0+3))+abs(5-(0+4))+abs(5-(0+5))=2. Any choice\nof b does not make the sadness of Snuke less than 2, so the answer is 2.\n\n* * *"}, {"input": "9\n    1 2 3 4 5 6 7 8 9", "output": "0\n    \n\n* * *"}, {"input": "6\n    6 5 4 3 2 1", "output": "18\n    \n\n* * *"}, {"input": "7\n    1 1 1 1 2 3 4", "output": "6"}]