fun readInt () =
    valOf (TextIO.scanStream (Int.scan StringCvt.DEC) TextIO.stdIn)

fun readStr () =
    let
        fun scan reader stream = SOME (StringCvt.splitl (not o Char.isSpace) reader (StringCvt.skipWS reader stream))
    in
        valOf (TextIO.scanStream scan TextIO.stdIn)
    end


fun findAns s1 s2 =
    let
        fun findAnsAux [] _ = 0
          | findAnsAux _ [] = 0
          | findAnsAux (h1::t1) (h2::t2) = 
            if h1 <> h2 then 1 + findAnsAux t1 t2
            else findAnsAux t1 t2
    in
        findAnsAux (String.explode s1) (String.explode s2)
    end


val () =
    let
        val n = readInt ()
        val s = readStr ()
        val t = readStr ()
                        
        val ans = findAns s t
    in
        print (Int.toString ans ^ "\n")
    end