'''Task:
Your task is to write a function which returns the sum of following series upto nth term(parameter).

Series: 1 + 1/4 + 1/7 + 1/10 + 1/13 + 1/16 +...
Rules:
You need to round the answer to 2 decimal places and return it as String.

If the given value is 0 then it should return 0.00

You will only be given Natural Numbers as arguments.

Examples:
SeriesSum(1) => 1 = "1.00"
SeriesSum(2) => 1 + 1/4 = "1.25"
SeriesSum(5) => 1 + 1/4 + 1/7 + 1/10 + 1/13 = "1.57"'''
from numpy import array


def series_sum(n):
    if n == 0:
        return "{:.2f}".format(n)

    den = [1]

    for i in range(n - 1):
        den.append(float(den[i] + 3))

    return "{:.2f}".format(sum(1 / (array(den))))
    # return str(round(series_sum, 2))


print(series_sum(0))
