Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Buddhists do not consider Siddhartha Gautama to have been the only Buddha. The Pali Canon refers to many previous ones (see List of the 28 Buddhas), while the Mahayana tradition additionally has many Buddhas of celestial, rather than historical, origin (see Amitabha or Vairocana as examples, for lists of many thousands Buddha names see Taishō Shinshū Daizōkyō numbers 439–448). A common Theravada and Mahayana Buddhist belief is that the next Buddha will be one named Maitreya (Pali: Metteyya).
How many Buddhas are considered to have existed in the Pali Canon?