program kadai
implicit none
integer  ::  n
integer,allocatable  ::  a(:)
integer  ::  i
integer  ::  shita
real(8)  ::  ans,ue

read(*,*) n
allocate(a(n))
read(*,*) a

do i=1,n
    ue=ue+1/real(a(i),8)
end do

ans=1/ue

write(*,*) ans

end program kadai
