python , use iteration

The Fibonacci sequence is a famous sequence in mathematics. The first element in the sequence is 0 and the second element is 1. The nth element is defined as F_n = F_n-1 + F_n-2.

Implement the fib function, which takes an integer n and returns the nth Fibonacci number. Use a while loop in your solution.

def fib(n):

"""Returns the nth Fibonacci number.

>>> fib(0)

0

>>> fib(1)

1

>>> fib(2)

1

>>> fib(3)

2

>>> fib(4)

3

>>> fib(5)

5

>>> fib(6)

8

>>> fib(100)

354224848179261915075

""" "*** YOUR CODE HERE ***"