open Printf
open Scanf

let solve s t =
  let l = String.length s in
  let rec loop ct i =
    if i = l then ct else
      if s.[i] = t.[i] then loop ct (i + 1)
      else loop (ct + 1) (i + 1) in
  loop 0 0

let () =
  scanf "%s %s " solve |> printf "%d\n"
