
class Solution:

    def recursive_fibonacci(self, num):
        if num < 0 or not isinstance(num, int):
            return
        elif num == 0 or num == 1:
            return num
        else:
            return self.regular_fibonacci(n - 1) + self.regular_fibonacci(n - 2)

    def iterative_fibonacci(self, num):
        if num < 0 or not isinstance(num, int):
            return

        f_first = 0
        f_second = 1
        f_sum = 0

        for i in range(num - 1):
            f_sum = f_first + f_second
            f_first = f_second
            f_second = f_sum

        return f_sum

