import qualified Data.ByteString as S
import System.Environment
import System.Exit
import System.IO
import Data.Char
main :: IO ()
main = do args <- getArgs
          case args of
            [i,inp,outp] | all isDigit i -> do
              s <- if inp == "-" then S.getContents else S.readFile inp
              S.writeFile outp $ S.append s $ S.replicate (read i - S.length s) 0
            _ -> do hPutStrLn stderr "Usage: pad <number> <input-file> <output-file>"
                    exitFailure