output_description: Print the number of positive integers less than or equal to N that have an odd
  number of digits.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: S = list(input())
  line = []
  A = ["A", "C", "G", "T"]
  num_list = []
  flag = False
  for s in S:
      if s in A:
          line.append(s)
          flag = True
      elif flag:
          num_list.append(len(line))
          line = []
          flag = False
  num_list.append(len(line))
  if len(num_list) == 0:
      print(0)
  else:
      print(max(num_list))
  
problem_description: Statement
  
  Given is an integer N. Find the number of positive integers less than or equal
  to N that have an odd number of digits (in base ten without leading zeros).
samples: [{"input": "11", "output": "9\n    \n\nAmong the positive integers less than or equal to 11, nine integers have an\nodd number of digits: 1, 2, \\ldots, 9.\n\n* * *"}, {"input": "136", "output": "46\n    \n\nIn addition to 1, 2, \\ldots, 9, another 37 integers also have an odd number of\ndigits: 100, 101, \\ldots, 136.\n\n* * *"}, {"input": "100000", "output": "90909"}]