# Even Fibonacci numbers

# 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 sum_of_even_fibs_up_to(n)
  a, b = 1, 2
  sum = 0
  while a < n + 1
    # puts(a) # little test
    sum += a if a % 2 == 0
    c = a
    a = b
    b += c
  end
  return sum
end
puts(sum_of_even_fibs_up_to(100))
puts(sum_of_even_fibs_up_to(4_000_000))