defmodule Main do
  def main do
    s=IO.gets("") |> String.trim()
    t=IO.gets("") |> String.trim()
	  Enum.to_list(0..(String.length(s)-1))
    |>Enum.map(fn x -> String.at(s,x)==String.at(t,x) end)
    |>Enum.count(fn x -> x==false end)
    |>IO.puts()
    end
end
