import qualified Data.ByteString.Char8 as BS
import Control.Monad
import Data.Char
import Data.List


-- space delimited integers
getVals::IO [Int]
getVals = unfoldr (BS.readInt . BS.dropWhile isSpace) <$> BS.getLine

-- space delimited strings
getStrings::IO [String]
getStrings = (map BS.unpack . BS.words) <$> BS.getLine


solver :: String -> Int
solver ls = div (length $ filter (\ (a,b) ->a/=b) $ zip ls $ reverse ls) 2


main::IO()
main = print.solver =<< getLine