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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 mark_received(self, visibility_timeout=None):
 """ When a message is received we will set the first receive timestamp, tap the ``approximate_receive_count`` and the ``visible_at`` time. """

        if visibility_timeout:
            visibility_timeout = int(visibility_timeout)
        else:
            visibility_timeout = 0

        if not self.approximate_first_receive_timestamp:
            self.approximate_first_receive_timestamp = int(unix_time_millis())

        self.approximate_receive_count += 1

        # Make message visible again in the future unless its
        # destroyed.
        if visibility_timeout:
            self.change_visibility(visibility_timeout)

        self.receipt_handle = generate_receipt_handle()