Problem 25
http://projecteuler.net/index.php?section=problems&id=25
何番目のフィボナッチ数が最初に1000ケタを越えるのか?
import Sequence (fib) main = print $ head $ filter (\(_, s) -> length s >= 1000) $ zip [1..] $ map show fib
module Sequence (fib) where fib = fib' 1 1 fib' a b = a : fib' b (a + b)