You will be given a definition of a task first, then some input of the task.
This task involves annotating the answer type to a given question that involve some kind of complex reasoning (including numerical reasoning). Note that the questions require looking at more than one part of the passage to answer. There are 3 possible answer types (i) spans, (ii) numbers and (iii) dates. If the answer can be found in the passage, label it as "span". If the answer is a number, label as "number". Similarly, label "date" if you think the answer to the given question is a date.

Passage: Knopf was founded in 1915 by Alfred A. Knopf Sr. along with Blanche Knopf, on a $5,000 advance from his father, Samuel Knopf. The first office was located in New York's Candler Building. The publishing house was officially incorporated in 1918, with Alfred Knopf as president, Blanche Knopf as vice-president, and Samuel Knopf as treasurer. From the start, Knopf focused on European translations and high-brow works of literature. Among their initial publications were French author Emile Augier's Four Plays, Russian writer Nikolai Gogol's Taras Bulba, Polish novelist Stanisaw Przybyszewski's novel Homo Sapiens, and French writer Guy de Maupassant's Yvette, a novelette, and Ten Other Stories. During World War I these books were cheap to obtain and helped establish Knopf as an American firm publishing European works. Their first bestseller was a new edition of Green Mansions, a novel by W. H. Hudson which went through nine printings by 1919 and sold over 20,000 copies. Their first original American novel, The Three Black Pennys by Joseph Hergesheimer, was published in 1917.
Question: How many years were there between the founding of Knopf and their first best seller?
Output:
number