program main
  implicit none
  integer i,N
  real(8) ans
  real(8),allocatable :: A(:)
  read(*, *) N
  allocate(A(N))
  read(*, *) (A(i), i = 1,N)
  ans = 0
  do i = 1,N
    ans = ans + (1/A(i))
  end do

  write(*, *) 1/ans
end program main
