public Slider Brightness;
    public float bri,briv; // only briv value I saving it.

    // Use this for initialization
    void Start () {
        PlayerPrefs.GetFloat("briv");
        Brightness.value = briv;
        }

    void Update() {
            briv = bri;
            bri = Brightness.value;

    if (Input.GetKeyDown(KeyCode.S)) {
        PlayerPrefs.SetFloat("briv",briv);
        Debug.Log ("save");
    }

        } // end update