Optimized Fibonacci

def fib(n):
    I = [[1, 1], [1, 0]]
    if (n == 0):    return 0
    power(I, n - 1)
    return I[0][0]
def multiply(I, A):
    x = (I[0][0] * A[0][0] + I[0][1] * A[1][0])
    y = (I[0][0] * A[0][1] + I[0][1] * A[1][1])
    z = (I[1][0] * A[0][0] + I[1][1] * A[1][0])
    w = (I[1][0] * A[0][1] + I[1][1] * A[1][1])
    I[0][0], I[0][1], I[1][0], I[1][1] = x, y, z, w
def power(I, n):
    if (n == 0 or n == 1):
        return
    A = [[1, 1],  [1, 0]]
    power(I, n // 2)
    multiply(I, I)
    if (n % 2 != 0):
        multiply(I, A)