program main
  implicit none
  integer :: n, i
  integer, allocatable :: a(:)
  real(8), allocatable :: ar(:)
  read (*, *) n
  allocate (a(n), ar(n))
  read (*, *) a(:)
  ar(:) = 1.0 / dble(a(:))
  write (*, *) 1.0 / sum(ar)
end program main

