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

let inline fib n =
    let rec iter pp p c =
        if c = LanguagePrimitives.GenericZero then pp
        else iter p (pp ^^^ p) (c - LanguagePrimitives.GenericOne)
    iter n0 n1 n

fib n |> printfn "%d"