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

toYesNo :: Bool -> String
toYesNo True = "yes"
toYesNo _ = "no"

isAllDifferent :: String -> Bool
isAllDifferent "" = True
isAllDifferent (x:xs)
    | elem x xs = False
    | otherwise = isAllDifferent xs

solve :: String -> String
solve = toYesNo . isAllDifferent

main :: IO ()
main = do
    s <- getLine
    putStrLn $ solve s
