text: """
  File: complement.py
  Name:
  ----------------------------
  This program uses string manipulation to
  tackle a real world problem - finding the
  complement strand of a DNA sequence.
  THe program asks uses for a DNA sequence as
  a python string that is case-insensitive.
  Your job is to output the complement of it.
  """
  
  
  def main():
      """
      1. input a DNA string
      2. make sure all DNA alphabets will be upper
      3. turn A <=> T & C <=> G
      4. print the new DNA
      """
      dna = input('Please give me a DNA　strand and I\'ll find the complement: ')
      dna = dna.upper()
      new_dna = build_complement(dna)
      print('The complement of ' + dna + ' is ' + new_dna)
  
  
  def build_complement(dna):
      """
      turn A <=> T & C <=> G
      """
      ans = ""
      for base in dna:
          if base == 'A':
              ans += 'T'
          if base == 'T':
              ans += 'A'
          if base == 'G':
              ans += 'C'
          if base == 'C':
              ans += 'G'
      return ans
  
  
  
  
  
  
  ###### DO NOT EDIT CODE BELOW THIS LINE ######
  if __name__ == '__main__':
      main()
  