"""
Project Euler - 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.
"""


def fibonacci_even_sum(n):
    p = 1
    c = 1
    total = 0
    while c <= n:
        p = c - p
        c = p + c
        if c % 2 == 0:
            total += c
    return total


print(fibonacci_even_sum(4000000))
