open System

let rec josephus = 
    function
        | 1 -> 1
        | x  -> (if x % 2 <> 0 then 1 else -1) + 2 * josephus (x / 2)

let josephus' (target: int): int =
    let pow = Math.Pow(3, Math.Floor(Math.Log(target, 3))) |> int
    if pow = target then pow
    else if pow >= target / 2 then target - pow
    else pow + (2 * (target - 2 * pow))

josephus 3017957 |> printfn "%d"
josephus' 3017957  |> printfn "%d"