def sum_all_multiples(cutoff):
    """Return the answer to the answer above.

    Parameters:
    cutoff -- int: the value under which we are summing values of 3 and 5

    Return: int - sum of all multiples of 3 and 5 below cutoff.
                  Only natural numbers are included in the sum.

    """
    sum = 0
    for i in range(1, cutoff):
        if i % 3 == 0 or i % 5 == 0:
            sum += i
    return sum