Task: Question Understanding
Input (English): Passage: Anaukpetlun would not spend his scarce resources on subjugating Siam. His strategy was to pick off Siam's peripheral regions rather than launch a full-scale invasion. On 30 November 1613, he sent a small army of 4,000  to drive out the Siamese from upper Tenasserim coast. On 26 December 1613, the army defeated the Siamese at Tavoy. The Burmese followed down to Tenasserim port itself. But the Burmese were driven back with heavy losses by the wealthy port's Portuguese broadsides in March 1614. The Siamese tried to retake Tavoy but failed. Anaukpetlun then switched theatres to Lan Na, which like Martaban before was only a nominal vassal of Siam. His armies of 17,000 invaded Lan Na on 30 April 1614 from Martaban in the south and Mone in the north. Lan Na's ruler, Thado Kyaw, desperately sought help. Help came from Lan Xang, not his overlord Siam. Despite the logistical troubles and the rainy season conditions, the Burmese armies finally achieved encirclement of Lan Na and Lan Xang forces in the Chiang Mai and Lanphun pocket in August 1614. After nearly five months, on 22 December 1614, the city surrendered. Siam would not make any attempts to recover Lan Na until 1663.
Question: How many months after the invasion of Lan Na did the city surrender?
Output (English): number