Task: Question Generation
Input (English): Passage: After the Lithuanians were defeated in the Battle of Strėva by the Teutonic Knights in 1348, Liubartas lost all territories except for eastern Volhynia with Lutsk to Casimir and his ally Louis I of Hungary . Liubartas' brothers Algirdas and Kęstutis organized several expeditions to Poland and Red Ruthenia. Lithuanians allied themselves with Muscovy: Liubartas married an unnamed daughter of Konstantin of Rostov, a relative of Simeon of Moscow, and Algirdas married Uliana of Tver, sister-in-law of Simeon. In spring 1351, Lubartas was taken prisoner by Louis, but was released in summer after a truce was agreed upon with Kęstutis. The deal fell through and more military attacks followed in 1352. Another truce, rather favorable to the Lithuanians, was signed in fall 1352: Lubartas received not only Volhynia and Podolia, but also Belz and Chełm. However, already in 1353, Liubartas attacked again. Casimir responded by organizing a large campaign against the pagan Lithuanians with a special permission from Pope Innocent VI. After the campaign did not achieve the desired results, Casimir contemplated an alliance with the Lithuanians. In 1366, Casimir, allied with Siemowit III of Masovia and nephews of Liubartas, resumed the war. As Algirdas was involved in conflicts in the east and Kęstutis fought with the Teutonic Knights, Liubartas had to defend alone and was defeated. In fall 1366, a treaty was signed: Liubartas retained only eastern Volhynia with Lutsk and became somewhat dependent on Poland . Casimir awarded his allies: Yuri, son of Karijotas, received Chełm, his brother Alexander received Volodymyr-Volynskyi, and Yuri, son of Narimantas, continued to rule Belz.
Output (English): How many brothers did Liubartas have?