Task: Question Understanding
Input (English): Passage: On 7-8 October at the Battle of Slobodyshche 14,000-15,000 Poles and 5,000-6,000 Tatars defeated the Cossacks under Yurii Khmelnytsky, who was trying to link up with Sheremetev. After the unsuccessful battle Yurii began talks with the Poles. As a result, he broke the alliance with Moscow and 17 October signed Slobodischensky Tacktat, under which the Hetmanate rejoined the Commonwealth. After learning of this switch, Tsetsyura and his Cossacks, who were with Sheremetev, also changed sides . This left Sheremetev, who was defending Chudnov in a dangerous position. At the Battle of Chudnov the Poles defeated the Russians . The fortified Russo-Cossack camp was completely encircled. During the battle Tsetsyura went over to the royal army with 2,000 Cossacks. However, most of the Left-Bank Cossack regiments remained the loyal to Moscow. .) The 15,000-man  Russian army was completely surrounded. Prince Yuri Baryatinsky left Kiev to help Sheremetev, but was stopped at Brusilov by Polish cavalry under Jan Sobieski. The Russians made unsuccessful forays from the besieged camp, but could not change anything. On 4 November Sheremetev was forced to capitulate. The disarmed Russian soldiers were released. The price was high: the Russians had to pay 300,000 rubles and evacuate Kiev, Pereyaslav, Chernigov. Sheremetev remained in captivity. On the night of 4-5 November, as soon as the 10,000 Russians gave up their weapons, the Tatars broke into the camp and started grabbing people with lassos. The disarmed Russians defended themselves as well as they could, but the Tatars killed many with arrows and took about 8,000 prisoners. Yielding to a demand, the Poles gave Sheremetev to the Tatars. The Russians and Left-Bank Cossacks lost 4,200 killed, 4,000 wounded and 20,500 captives.
Question: Who was the leader of the Polish cavalry?
Output (English): span