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: moji = str(input())  # 文字列の入力
  ListNum = []  # suuの各値を入れる
  suu = 0
  for i in range(0, len(moji), 1):
      if moji[i] == "A":
          suu += 1
      elif moji[i] == "T":
          suu += 1
      elif moji[i] == "G":
          suu += 1
      elif moji[i] == "C":
          suu += 1
      else:
          ListNum.append(suu)
          suu = 0
  print(max(ListNum))
  
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)."}]