def series_sum(n):
    if n == 0 or n == 1:
        return str(n) + ".00"
    denominator = 4
    algo = 1
    for i in range(n - 1):
        algo += 1/denominator
        denominator += 3
    if len(str(round(algo, 2))) == 3:
        return str(round(algo, 2)) + "0"
    return str(round(algo, 2))
