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()
  L = len(S)
  longest = 0
  for i in range(L):
      for j in range(i + 1):
          DUP = S[j:i]
          DUP = DUP.replace("A", "#")
          DUP = DUP.replace("T", "#")
          DUP = DUP.replace("G", "#")
          DUP = DUP.replace("C", "#")
          count = 0
          for a in range(len(DUP)):
              if DUP[a] == "#":
                  count += 1
              else:
                  break
          else:
              longest = max(longest, count)
  print(longest)
  S = input()
  L = len(S)
  longest = 0
  for i in range(L):
      for j in range(i + 1):
          DUP = S[j : i + 1]
          DUP = DUP.replace("A", "#")
          DUP = DUP.replace("T", "#")
          DUP = DUP.replace("G", "#")
          DUP = DUP.replace("C", "#")
          count = 0
          for a in range(len(DUP)):
              if DUP[a] == "#":
                  count += 1
              else:
                  break
          else:
              longest = max(longest, count)
  print(longest)
  
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"}]