Task: Question Understanding
Input (English): Passage: On 17 August, Medvedev announced that Russian forces would begin to pull out of Georgia the following day. The two countries exchanged prisoners of war on 19 August. A Georgian official said that although his country exchanged five Russian servicemen for fifteen Georgians, among them two civilians, Georgia suspected that Russia still held two more Georgians. On 22 August, Russian forces withdrew from Igoeti and the Georgian police proceeded towards Gori. Russia claimed that its military withdrawal was completed; however, Russian checkpoints remained near Gori and two Russian lookout stations remained near Poti. On 13 September, Russian troops began withdrawing from western Georgia and by 11:00 Moscow Time, the posts near Poti were abandoned. Withdrawals from Senaki and Khobi also took place. Russian forces withdrew from the buffer zones adjacent to Abkhazia and South Ossetia on 8 October and authority over them was transferred to the European Union monitoring mission in Georgia. Russia continued to maintain a single checkpoint in the border village of Perevi. On 12 December, Russian forces withdrew; eight hours later they re-entered the village and Georgian police withdrew after the Russians threatened to fire. Russian forces then set up three checkpoints in the village. On 18 October 2010 all Russian troops in Perevi withdrew to South Ossetia and a Georgian Army unit moved in. On 9 September 2008, Russia announced that its troops in South Ossetia and Abkhazia would remain under bilateral agreements with their respective de facto governments. Russian Foreign Minister Sergey Lavrov said that a military presence in Abkhazia and South Ossetia was essential to prevent Georgia from regaining control. Georgia considers Abkhazia and South Ossetia Russian-occupied territories. In November 2011, the European Parliament passed a resolution recognising Abkhazia and South Ossetia as occupied Georgian territories.
Question: How many days after Medvedev announced Russian forces would begin to pull out of Georgia did the two countries exchange prisoners of war?
Output (English): number