solve :: String -> String -> Int -> Int
solve s t ans
 | (length s == 0) = ans
 | otherwise       = solve (tail s) (tail t) newAns
  where newAns = ans + if (head s) == (head t) then 0 else 1

main :: IO ()
main = do 
 s <- getLine :: IO String
 t <- getLine :: IO String
 print $ solve s t 0