def qfib(n: Int) = {

    match n {
        case 1 => 1
        case 2 => 3
        case 3 => 5
        case _ => tail_qfib(n, 1, 3, 5, 0)
    }

    def tail_qfib(n: Int, a: Int, b: Int, c: Int, acc: Int) = {
        match n {
            case 0 => acc
            case _ => tail_qfib(n-1, b, c, acc, 3 * c + 2 * b - a)
        }

    }
}