练习题来源:
https://projecteuler.net/archives
Problem 2
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, ...
By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.
问题2：
斐波那契数列的规则是：后一个数字是前两个数字之和，如前十个斐波那契数列为:
1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
那么根据其规律，找出400，0000以内的斐波那契数，计算其偶数之和
