output_description: Print the letter representing the base that bonds with the base b.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      b
attempt: s = input()
  le = len(s)
  lis = []
  for i in range(0, le):
      if s[i] != "A" and s[i] != "" and s[i] != "T" and s[i] != "G":
          lis.append(i)
  lo = 0
  for j in range(0, len(lis) - 1):
      if lis[j + 1] - lis[j] - 1 >= lo:
          lo = lis[j + 1] - lis[j] - 1
  if lis[0] >= lo:
      lo = lis[j]
  if len(lis) - lis[-1] + 1 >= lo:
      lo = len(lis) - lis[-1] - 1
  print(lo)
  
problem_description: Statement
  
  On the Planet AtCoder, there are four types of bases: `A`, `C`, `G` and `T`.
  `A` bonds with `T`, and `C` bonds with `G`.
  
  You are given a letter b as input, which is `A`, `C`, `G` or `T`. Write a
  program that prints the letter representing the base that bonds with the base
  b.
samples: [{"input": "A", "output": "T\n    \n\n* * *"}, {"input": "G", "output": "C"}]