cost :: Int -> Int
cost x = (x `div` 3) - 2

fuel :: Int -> [Int]
fuel x
    | cost x <= 0 = []
    | otherwise = cost x : fuel (cost x)

totalCost :: Int -> Int
totalCost = sum . fuel

main :: IO ()
main = do
    ls <- map read <$> lines <$> readFile "day1.txt"
    print $ sum $ map totalCost ls