import math

SQRT_5 = math.sqrt(5)
GOLDEN_NUMBER = (1 + SQRT_5) / 2

"""
Fibonacci number is described as follows:
Fn = 1 / sqrt(5) (pow(a,n) – pow(b,n))
where: a = 1 / 2 (1 + sqrt(5)) and b = 1 / 2 (1 – sqrt(5))
"""
def fib(n):
    return int(1 / SQRT_5 * (GOLDEN_NUMBER ** n - (-1 / GOLDEN_NUMBER) ** n))

print(fib(10))