In this task, you're given a passage, further information available on a particular linked term from the statement, and a question. Your job is to generate the answer to the question by using the information provided. If there is no clear answer obtainable, output 'none'.
Q: Passage: It was originally constructed by the Teutonic Knights, a German Catholic religious order of crusaders, in a form of an Ordensburg fortress. The Order named it Marienburg in honour of Mary, mother of Jesus. In 1457, during the Thirteen Years' War, it was sold by the Bohemian mercenaries to King Casimir IV of Poland in lieu of indemnities and it since served as one of the several Polish royal residences and the seat of Polish offices and institutions, interrupted by several years of Swedish occupation, and fulfilling this function until the First Partition of Poland in 1772. From then on the castle was under German rule for over 170 years. Following Germany's defeat in World War II in 1945, the land was assigned to Poland by the Allies. Heavily damaged, the castle was renovated under the auspices of modern-day Poland in the second half of the 20th century and most recently in 2016. Nowadays, the castle hosts exhibitions and serves as a museum.
Link Information: Children.- Vladislaus (1 March 1456 - 13 March 1516) Question: How many children did King Casimir IV have when he purchased Malbork Castle from the Teutonic Knights?
A:
Answer: 2