import System.Environment
import Control.Monad
main :: IO ()
main = do
  argc <- length `fmap` getArgs
  when (argc /= 0) . fail . unlines $ ["summ does not expect arguments."
                                      ,"It reads numbers from stdin and finally prints the sum"]
  print . sum               -- sum them up
        . map readI         -- turns numbers into integers
        . concatMap words   -- split words
        . lines             -- split lines
        =<< getContents     -- reads stdin
  where readI :: String -> Integer
        readI = read