let xorFib n f0 f1 =
  let rec f n ``f_n-2`` ``f_n-1`` =
    match n with
    | 0L -> ``f_n-2``
    | _ -> f (n-1L) ``f_n-1`` (``f_n-2``^^^``f_n-1``)
  f n f0 f1

let f0, f1, n =
  let t = stdin.ReadLine().Split() |> Array.map int64
  t.[0], t.[1], t.[2]

xorFib (n%3L) f0 f1
|> stdout.WriteLine