program res
  implicit none
  integer,allocatable :: A(:)
  integer :: N,i
  real(16) :: S,Si

  read(*,*) N
  allocate(A(N))
  read(*,*) A
  S=0.0_16
  do i=1,N
     S=S+1.0_16/A(i)
  enddo
  Si=1.0_8/S
  if(Si.lt.10.0_16) then
    write(*,'(f10.8)') Si
  elseif(Si.lt.100.0_16) then
    write(*,'(f11.8)') Si
  elseif(Si.lt.1000.0_16) then
    write(*,'(f12.8)') Si
  else
    write(*,'(f13.8)') Si
  endif

end program res