Teacher: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'.
Teacher: Now, understand the problem? Solve this instance: Passage: In 1014, after decades of war, the Byzantine Emperor Basil II scored a decisive victory over the Bulgarian Emperor Samuil in the battle of Kleidion. Samuil died of a heart attack on 6 October 1014 and the Byzantines took the opportunity to penetrate deep into Macedonia, the political heart of the Bulgarian Empire, and seized a number of important cities (Bitola, Prilep, Voden, Maglen). After the new Bulgarian Emperor Ivan Vladislav, who in 1015 assassinated Samuil's son and heir Gavril Radomir, had unsuccessfully tried to make an agreement with Basil II, he organized the defense of the country. The Bulgarians led by the Emperor, Krakra of Pernik and Ivats managed to return a number of towns and castles. The Byzantines were defeated in the battle of Bitola (September 1015) and at the siege of Pernik (summer of 1016).
Link Information: The First Bulgarian Empire (Old Bulgarian: , ts'rstvo bl'garskoe) was a medieval Bulgarian state that existed in Southeastern Europe between the 7th and 11th centuries AD. Question: How long did the state entity that Macedonia was the political heart of last?
Student:
Answer: 4