let solve s t =
  let len_s = String.length s in
  let rec solve' i result =
    if i >= len_s then
      result
    else
      let result =
        if s.[i] <> t.[i] then
          result + 1
        else
          result
      in
      solve' (i + 1) result
  in
  solve' 0 0

let () =
  let _ = read_line ()
  and s = read_line ()
  and t = read_line () in
  solve s t
  |> string_of_int
  |> print_endline