problem_two.rb

=begin
    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.
    
    http://projecteuler.net/problem=2
=end

sum, before, now = 0, 1, 1

while now < 4_000_000
    before, now = now, now + before
    sum += now if now % 2 == 0
end

puts sum