def fibonacci(nth_fib):
    """ (int) -> int
    
        where <nth_fib> is a positive integer,
        Returns the <nth_fib> Fibonacci number
    """
    if isinstance(nth_fib, int):
        if nth_fib < 0:
            return 0
        elif nth_fib == 1:
            return 1
        else:
            return fibonacci(nth_fib - 2) + fibonacci(nth_fib - 1)
    else:
        return 'Expected Integer'