Task: Question Answering
Input (English): Passage: On 12 February 2017, a series of riots began across the Khuzestan province continuing for about a week. Protesters reportedly expressed solidarity  with fellow countrymen, chanting slogans against the Iranian government. Initially the protests were targeted against lack of vital daily services, but the atmosphere quickly grew political with the crowd beginning to chant "Death to tyranny," "Death to repression," "We the people of Ahvaz will not accept oppression," Expel incompetent officials," "Ahwaz is our city, clean air is our right," and "Shame on state police." Iranian government responded to the unrest by issuing a statement warning people to refrain from "illegal gatherings" and serious action will be taken against any and all violators. Riot police units were dispatched to the city of Ahwaz, in addition to additional forces from neighboring provinces. Iranian authorities banned many Western reporters from visiting the city. Exiled leader of an Iranian opposition group Maryam Rajavi hailed the people of Khuzestan, while calling on all Iranians to rise in support. In early April 2017, Ahwazi activist killed by Basij militia in Ma'shour city On 15 May 2017, suspected Arab separatist gunmen killed two police officers in Ahvaz. On October 2017, Ahmad Mullah Nissi, head of the Arab Struggle Movement for Khuzestan was assassinated in the Netherlands. 
Question: how many months after the riots began across the Khuzestan province were two police officers in Ahvaz killed by separatist gunment? 
Answer type: Number 
Output (English): 3.