Other people already corrected you, but I feel like being obtuse so here it goes. The circle goes from Jamaica, along Queens Blvd, down 8th Ave to W 4th St, along the F line to Jay St, down Fulton St to Broadway Junction, past Cypress hills on the Nassau line (J/Z), and finally returns to Jamaica. This loop is possible without adding any additional tracks or switches to the system. Thats how the pigeon flies. Checkmate.