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    private static Optional<S3ObjectSummary> findLatestCSVFile(AmazonS3 s3Client) {
        ListObjectsV2Request req = new ListObjectsV2Request().withBucketName(BUCKET_NAME).withPrefix(PREFIX);
        ListObjectsV2Result result;

        List<S3ObjectSummary> csvFiles;
        do {
            result = s3Client.listObjectsV2(req);
            csvFiles = result.getObjectSummaries().stream()
                    .filter(obj -> obj.getKey().endsWith(".csv"))
                    .collect(Collectors.toList());

            String token = result.getNextContinuationToken();
            req.setContinuationToken(token);
        } while (result.isTruncated());

        return csvFiles.stream()
                .max(Comparator.comparing(S3ObjectSummary::getLastModified));
    }