program test
implicit none
integer::i,N
real(8)::ans
real(8),allocatable::a(:)
ans=0
read*,N
allocate(a(N))
read(*,*)(a(i),i=1,N)
    	do i=1,N
        	ans=ans+1.0/a(i)
        end do
ans=1.0/ans
print*,ans
end program test