fib.py

def fib(n):
    """Calculate the Nth fibonacci number.
    
    Intentionally don't use dynamic programming. Goal is to simulate a long-running task.
    """
    if n < 0:
        raise ValueError('Negative numbers are not supported')
    elif n == 0:
        return 0
    elif n <= 2:
        return 1

    return fib(n - 2) + fib(n - 1)