output_description: Print the length of the longest _ACGT string_ that is a substring of S.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      S
attempt: def tasu(i):
      global bubun
      if i >= len(string):
          return
      elif string[i] == "A" or string[i] == "C" or string[i] == "G" or string[i] == "T":
          bubun += string[i]
          tasu(i + 1)
  
  
  string = input()
  
  lst = [""]
  
  for i in range(len(string)):
      if string[i] == "A" or string[i] == "C" or string[i] == "G" or string[i] == "T":
          bubun = ""
          tasu(i)
          lst.append(bubun)
  
  print(len(max(lst)))
  
problem_description: Statement
  
  You are given a string S consisting of uppercase English letters. Find the
  length of the longest _ACGT string_ that is a substring (see Notes) of S.
  
  Here, a ACGT string is a string that contains no characters other than `A`,
  `C`, `G` and `T`.
samples: [{"input": "ATCODER", "output": "3\n    \n\nAmong the ACGT strings that are substrings of `ATCODER`, the longest one is\n`ATC`.\n\n* * *"}, {"input": "HATAGAYA", "output": "5\n    \n\nAmong the ACGT strings that are substrings of `HATAGAYA`, the longest one is\n`ATAGA`.\n\n* * *"}, {"input": "SHINJUKU", "output": "0\n    \n\nAmong the ACGT strings that are substrings of `SHINJUKU`, the longest one is\n`` (the empty string)."}]