# 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.
x, y, sum = 1, 1, 0
while sum < 4000000
sum += (x + y)
x, y = x + 2*y, 2*x + 3*y
end
puts "Answer: #{ sum }."