let rec srednia_geometryczna (ilosc:int) (suma:double) =
    let znak = System.Console.Readline()
    let wartosc = System.Convert.ToDouble(znak)
    if wartosc = 0.0 then (
        if ilosc <> 0 then (suma, System.Math.Pow(suma, (1.0 / double ilosc)))
                        else (0.0, System.Double.NaN)
                        )
    else srednia (ilosc + 1) (suma + wartosc)