<Table> <Tr> <Th_colspan="2"> "Crisis on Earth - X" </Th> </Tr> <Tr> <Td_colspan="2"> Arrowverse crossover event </Td> </Tr> <Tr> <Td_colspan="2"> Promotional poster and home media cover </Td> </Tr> <Tr> <Th> Episode nos . </Th> <Td> <Ul> <Li> Supergirl (part 1) </Li> <Li> Season 3, Episode 8 </Li> <Li> Arrow (part 2) </Li> <Li> Season 6, Episode 8 </Li> <Li> The Flash (part 3) </Li> <Li> Season 4, Episode 8 </Li> <Li> Legends of Tomorrow (part 4) </Li> <Li> Season 3, Episode 8 </Li> </Ul> </Td> </Tr> <Tr> <Th> Directed by </Th> <Td> <Ul> <Li> Larry Teng (Supergirl) </Li> <Li> James Bamford (Arrow) </Li> <Li> Dermott Downs (Flash) </Li> <Li> Gregory Smith (LoT) </Li> </Ul> </Td> </Tr> <Tr> <Th> Story by </Th> <Td> <Ul> <Li> Andrew Kreisberg </Li> <Li> Marc Guggenheim </Li> </Ul> </Td> </Tr> <Tr> <Th> Teleplay by </Th> <Td> <Ul> <Li> Robert Rovner (Supergirl) </Li> <Li> Jessica Queller (Supergirl) </Li> <Li> Wendy Mericle (Arrow) </Li> <Li> Ben Sokolowski (Arrow) </Li> <Li> Todd Helbing (Flash) </Li> <Li> Phil Klemmer (LoT) </Li> <Li> Keto Shimizu (LoT) </Li> </Ul> </Td> </Tr> <Tr> <Th> Original air dates </Th> <Td> <Ul> <Li> November 27, 2017 (2017 - 11 - 27) (1 & 2) </Li> <Li> November 28, 2017 (2017 - 11 - 28) (3 & 4) </Li> </Ul> </Td> </Tr> <Tr> <Th_colspan="2"> Episode chronology </Th> </Tr> <Tr> <Td_colspan="2"> <Table> <Tr> <Td_colspan="2"> Supergirl </Td> </Tr> <Tr> <Td> ← Previous "Wake Up" </Td> <Td> Next → "Reign" </Td> </Tr> <Tr> <Td_colspan="2"> List of Supergirl episodes </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Td_colspan="2"> Arrow </Td> </Tr> <Tr> <Td> ← Previous "Thanksgiving" </Td> <Td> Next → "Irreconcilable Differences" </Td> </Tr> <Tr> <Td_colspan="2"> List of Arrow episodes </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Td_colspan="2"> The Flash </Td> </Tr> <Tr> <Td> ← Previous "Therefore I Am" </Td> <Td> Next → "Don't Run" </Td> </Tr> <Tr> <Td_colspan="2"> List of The Flash episodes </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Td_colspan="2"> Legends of Tomorrow </Td> </Tr> <Tr> <Td> ← Previous "Welcome to the Jungle" </Td> <Td> Next → "Beebo the God of War" </Td> </Tr> <Tr> <Td_colspan="2"> List of Legends of Tomorrow episodes </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Th> Preceded by </Th> <Td> "Invasion!" </Td> </Tr> <Tr> <Th> Followed by </Th> <Td> "Elseworlds" </Td> </Tr> </Table> <Tr> <Th_colspan="2"> "Crisis on Earth - X" </Th> </Tr>

How many parts are in crisis on earth x
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