def antisense(s):
  """Return the antisense sequence for a DNA sequence
  >>> antisense('AGCACCTAGGCAATT')
  'TCGTGGATCCGTTAA'
  """
  r = []
  for c in s:
    i = 'ACGT'.find(c)
    if i < 0: raise "Invalid nucleotide"
    r.append('ACGT'[~i])
  return ''.join(r)

def _test():
  import doctest,dna
  return doctest.testmod(dna)

# Make into a program that can decode a message from stdin:

if __name__ == '__main__':
  _test()
  import sys
  for ln in sys.stdin:
    print antisense(ln.strip())