import qualified Data.ByteString.Char8 as BS
import Data.Maybe (fromJust)
import Control.Monad
import Data.List
import Debug.Trace

solve :: Int -> Int -> String
solve a b
    | a + b < 10 = show (a + b)
    | otherwise = "error"

main :: IO ()
main = do
    [a, b] <- map (fst . fromJust . BS.readInt) . BS.words <$> BS.getLine
    putStrLn $ solve a b
