def n_fib(n):
    """
    Find the nth Fibonacci Number.
    :param n: Nth element in the fibonacci series.
    :return: returns None if n is 0 otherwise returns the nth Fibonacci Number.
    """

    if n == 0:
        return None

    if n == 1 or n == 2:
        return n - 1

    a, b = 0, 1
    for i in range(2, n):
        a, b = b, a+b

    return b