Problem 2
Even Fibonacci numbers
Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with $1$ and $2$, the first $10$ terms will be:
$$1, 2, 3, 5, 8, 13, 21, 34, 55, 89, \ldots$$
By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.
偶斐波那契数
斐波那契数列中的每一项都是前两项的和。由$1$和$2$开始生成的斐波那契数列的前$10$项为：
$$1, 2, 3, 5, 8, 13, 21, 34, 55, 89, \ldots$$
考虑该斐波那契数列中不超过四百万的项，求其中为偶数的项之和。