我想限制刮到5页的数量与下面的代码，虽然该网站有50页。我在用Scrapy的爬行蜘蛛我怎么能这么做呢？

from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule

class BooksSpider(CrawlSpider):
    name = "bookscraper"
    allowed_domains = ["books.toscrape.com"]
    start_urls = ["https://books.toscrape.com/"]

    rules = (Rule(LinkExtractor(restrict_xpaths='//h3/a'), callback='parse_item', follow=True),
             Rule(LinkExtractor(restrict_xpaths='//li[@class="next"]/a'), follow=True),)

    def parse_item(self, response):

        product_info = response.xpath('//table[contains(@class, "table-striped")]')

        name = response.xpath('//h1/text()').get()
        upc = product_info.xpath('(./tr/td)[1]/text()').get()
        price = product_info.xpath('(./tr/td)[3]/text()').get()
        availability = product_info.xpath('(./tr/td)[6]/text()').get()

        yield {'Name': name, 'UPC': upc, 'Availability': availability, 'Price': price}