Instructions: In this task, you're given a question, along with a context passage which has extra information available on certain terms mentioned in it. Your job is to determine which sentence(s) from the passage can be used to search for further information needed to answer the question.
Input: Question: How old was King Henry IV when the Saxon Rebellion began? Passage:After the deposition of the Saxon duke Henry the Lion in 1180, the Regenstein counts were temporarily arrested by the forces of Emperor Frederick Barbarossa, but were reconciled with the Hohenstaufen monarch soon after. After a lengthy feud Heimburg Castle, built about 1170 by King Henry IV and soon after devastated during the Saxon Rebellion, was acquired by the Regenstein counts in the early 14th century. The Regenstein-Heimburg branch re-united the Regenstein and Blankenburg estates in 1343, under the rule of the most renowned Count Albert II (1310–49), who since the 1330s was frequently in dispute with the leaders of the surrounding estates like the Halberstadt bishops and the Abbesses of Quedlinburg; he was finally assassinated by the henchmen of Bishop Albert II of Halberstadt. These tales were romanticised in the ballad The Robber Count () by Gottfried August Bürger, melodized by Johann Philipp Kirnberger and the novel of the same name by Julius Wolff.

Output:
After a lengthy feud Heimburg Castle, built about 1170 by King Henry IV and soon after devastated during the Saxon Rebellion, was acquired by the Regenstein counts in the early 14th century