let solve a b =
  let rec solve' i result =
    if i > b then
      result
    else
      let result' =
        if (a + b + i) mod 3 = 0 then
          result + 1
        else
          result
      in
      solve' (i + 1) result'
  in
  solve' a 0

let () =
  let a, b =
    read_line ()
    |> fun l -> Scanf.sscanf l "%d %d" (fun a b -> (a, b))
  in
  solve a b
  |> Printf.printf "%d\n"