<Tr> <Th> Main contractor </Th> <Td> Skanska </Td> </Tr> <Tr> <Th_colspan="2"> References </Th> </Tr> <P> 30 St Mary Axe (informally known as the Gherkin and previously as the Swiss Re Building) is a commercial skyscraper in London's primary financial district, the City of London . It was completed in December 2003 and opened in April 2004 . With 41 stories it is 180 metres (591 ft) tall and stands on the former sites of the Baltic Exchange and Chamber of Shipping, which were extensively damaged in 1992 by the explosion of a bomb placed by the Provisional IRA in St Mary Axe, the street from which the tower takes its name . </P> <P> After plans to build the 92 - storey Millennium Tower were dropped, 30 St Mary Axe was designed by Norman Foster and Arup Group and it was erected by Skanska, with construction commencing in 2001 . </P>

How many floors are there in the gherkin