private void showAd()
    {
        int index = SceneManager.GetActiveScene().buildIndex;

        if (index % 2 == 0 && a)
        {
            admob.RequestRewardBaseVideo();
            admob.ShowRewardAd();
        }
    }
 private void OnRewardAdLoadedHandle()
 {
     //ad is loaded
     admob.ShowRewardAd();
 }