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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def encode(timestamp):
 """ Convert seconds since epoch to TAI64N string. @param timestamp: Seconds since UTC Unix epoch as C{float}. @return: TAI64N-encoded time, as C{unicode}. """

    seconds = int(timestamp)
    nanoseconds = int((timestamp - seconds) * 1000000000)
    seconds = seconds + _OFFSET
    encoded = b2a_hex(struct.pack(_STRUCTURE, seconds, nanoseconds))
    return "@" + encoded.decode("ascii")