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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 _get_offset_from_gcs(self):
 """Get the last offset that has been written to GCS. This is a utility method that does not modify self. Returns: an int of the last offset written to GCS by this upload, inclusive. -1 means nothing has been written. """

    headers = {'content-range': 'bytes */*'}
    status, response_headers, content = self._api.put_object(
        self._path_with_token, headers=headers)
    errors.check_status(status, [308], self._path, headers,
                        response_headers, content,
                        {'upload_path': self._path_with_token})
    val = response_headers.get('range')
    if val is None:
      return -1
    _, offset = val.rsplit('-', 1)
    return int(offset)