let n0, n1, n =
    stdin.ReadLine ()
    |> fun s -> s.Split ' '
    |> Array.map int64
    |> fun a -> (a.[0], a.[1], a.[2])

match n % 3L with
| 0L -> n0
| 1L -> n1
| _ -> n0 ^^^ n1
|> printfn "%d"