# 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.

N = 4000000

def fib_even(n):
    i0 = 1
    i = 1
    s = 0
    while i < n:
        if i % 2 == 0: 
            s += i
        aux = i
        i += i0
        i0 = aux
    return s

print(fib_even(N))
