Module Module1

    Sub Main()
        'Dim a As Integer
        'Dim s As String

        'a = Console.ReadLine()
        's = Console.ReadLine()

        'If a >= 3200 Then
        '    Console.WriteLine(s)
        'Else
        '    Console.WriteLine("red")
        'End If

        Dim n As Integer
        Dim a() As String
        Dim c As Integer
        Dim b As Double

        n = Console.ReadLine()

        a = Split(Console.ReadLine())

        For c = 0 To n - 1
            b = b + 1 / Integer.Parse(a(c))
        Next

        Console.WriteLine(1 / b)
    End Sub

End Module
