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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 GetPlasoTimestamp(self):
 """Retrieves a timestamp that is compatible with plaso. Returns: int: a POSIX timestamp in microseconds or None if no timestamp is available. """

    normalized_timestamp = self._GetNormalizedTimestamp()
    if normalized_timestamp is None:
      return None

    normalized_timestamp *= definitions.MICROSECONDS_PER_SECOND
    normalized_timestamp = normalized_timestamp.quantize(
        1, rounding=decimal.ROUND_HALF_UP)
    return int(normalized_timestamp)