require 'nokogiri'
require 'rest-client'
def get_title input
  begin
    if 0 == input.to_i
      res = RestClient.get input
    else
      res = RestClient.get "https://ruby-china.org/topics?page=#{input}"
    end
  rescue
    p "invalid url"
    return
  end
  doc = Nokogiri::HTML res.body
  doc.css('.title a').each do |i|
    p i.attributes['title'].value
  end
  p '-' * 100
end
puts 'Please input url, and enter "e" to exit.'
while 'e' != input = gets.chomp!
  get_title input
end