#!/usr/bin/env python
# coding: utf-8

# Every third fibonacci number is even. Since $F_n = F_{n-3} * 4 + F_{n-6}$, we initialy calculate $F_3$ and $F_6$ then $F_9 = F_6 * 4 + F_3$, $F_{12} = F_9 * 4 + F_6$ etc...

# In[15]:


def Fn(Fn_3, Fn_6):
    return Fn_3 * 4 + Fn_6
Fn_6 = 0
Fn_3 = 2
sum = Fn_6 + Fn_3
while True:
    f = Fn(Fn_3, Fn_6)
    if f > 4_000_000:
        break
    sum += f
    Fn_6 = Fn_3
    Fn_3 = f