one :: Int
one = one' 1000

one' :: Int -> Int
one' limit = sum $ filter valid [1..(limit - 1)] where
    valid :: Int -> Bool
    valid n = (n `mod` 3 == 0) || (n `mod` 5 == 0)

fibonnacci :: [Int]
fibonnacci = map fibonnacci_n [0..]

fibonnacci_n :: Int -> Int
fibonnacci_n 0 = 1
fibonnacci_n 1 = 1
fibonnacci_n n = fibonnacci_n (n-1) + fibonnacci_n (n-2)

two :: Int
two = sum [n | n <- takeWhile (<= 4000000) fibonnacci, n `mod` 2 == 0]