Given the task definition and input, reply with output. 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'.

Passage: Darius was the son of Hystaspes and the grandson of Arsames. Both men belonged to the Achaemenid tribe and were still alive when Darius ascended the throne. Darius justifies his ascension to the throne with his lineage. He claimed he could trace his ancestors back to Achaemenes, even though he was only distantly related. With this in mind, Darius married Atossa, daughter of Cyrus, with whom he had four sons: Xerxes, Achaemenes, Masistes and Hystaspes. He also married Artystone, another daughter of Cyrus, with whom he had two sons, Arsames and Gobryas. Darius married Parmys, the daughter of Bardiya, with whom he had a son, Ariomardus. Furthermore, Darius married Phratagune, with whom he had two sons, Abrokomas and Hyperantes. He also married another woman of the nobility, Phaidyme, the daughter of Otanes. It is unknown if he had any children with her. Before these royal marriages, Darius had married an unknown daughter of his good friend and lance carrier Gobryas from an early marriage, with whom he had three sons, Artobazanes, Ariabignes and Arsamenes. Any daughters he had with her are not known. Although Artobazanes was Darius's first-born, Xerxes became heir and the next king through the influence of Atossa; she had great authority in the kingdom as Darius loved her the most of all his wives.
Link Information: none Question: How long was he married to Artystone?
Answer: none