module Resistors_in_Parallel
  sub Main(ByVal args() as String)
    dim a as integer
    a=Console.ReadLine()
    dim arr() as integer
    arr=Split(Console.ReadLine())
    dim bb as double
    for i as integer = 0 to a
    bb+= 1/arr(i)
  next i
  dim ans as double = 1/bb

    Console.WriteLine(ans)
  end sub
end module