I know that the answer to the question "Who did Frederick II have to support to accept the Habsburgs?" is in "Austria was not able to retake Silesia or make any significant territorial gain. However, it did prevent Prussia from invading parts of Saxony. More significantly, its military performance proved far better than during the War of the Austrian Succession and seemed to vindicate Maria Theresa's administrative and military reforms. Hence, Austria's prestige was restored in great part and the empire secured its position as a major player in the European system. Also, by promising to vote for Joseph II in the Imperial elections, Frederick II accepted the Habsburg preeminence in the Holy Roman Empire. The survival of Prussia as a first-rate power and the enhanced prestige of its king and its army, however, was potentially damaging in the long run to Austria's influence in Germany.". Can you tell me what it is?
A:
Joseph II