Configure Huawei GK-1 and Huawei GK-2 as neighbor GKs. Terminal A and Terminal B are registered in GK-1, and Terminal C is registered in GK-2. If both GK-1 and GK-2 enable Q931 routing, and terminal A actively calls the number of terminal C and the call is successful, how many SETUP messages are used in the call process?

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