import Data.Char (isDigit)
import System.Environment (getArgs)
import System.IO (hPutStr,stderr)
import System.Exit (exitFailure)

nest :: Int -> String -> String
nest i = unlines . map (s++) . lines
  where s = replicate i ' '

main :: IO ()
main = do args <- getArgs
          case args of
            [arg] | all isDigit arg -> putStr . nest (read arg) =<< getContents
            _ -> do hPutStr stderr . unlines $
                      ["Usage: nest <number>"
                      ,""
                      ,"This program will write on standard output the contents"
                      ,"read on standard input but nested by <number> spaces."
                      ,""
                      ,"Each gets indented by <number> spaces more."
                      ]
                    exitFailure