Due to General Kangaroo's collapse while enhancing his combat abilities, he had to transform into the Cowardly Lizard.
General Kangaroo can choose to hide in one of the caves numbered $$$1$$$, $$$2$$$, $$$\dots$$$, $$$n$$$, while Kangaroo Splay will conduct $$$n$$$ probes on these $$$n$$$ caves. Fortunately, General Kangaroo knows the order in which Kangaroo Splay will probe the caves, so he can make a reasonable choice of hiding place to avoid detection.
For some reason, once General Kangaroo has chosen a hiding cave, he cannot change it. Please provide a cave number such that General Kangaroo can avoid all probes from Kangaroo Splay. If there are multiple feasible caves, output any one of them; if no such cave exists, output -1.
Formally, given a sequence of length $$$n$$$ denoted as $$$a_1, a_2, \dots, a_n$$$, you need to provide an $$$x(1\leq x \leq n)$$$ such that there is no $$$1 \leq i \leq n$$$ with $$$a_i = x$$$.
The input consists of multiple test cases.
First, an integer $$$T(1 \leq T \leq 1000)$$$ is given, indicating the number of test cases.
For each test case, first input an integer $$$n(1 \leq n \leq 2 \times 10^5)$$$, representing the number of caves and the number of probes by Kangaroo Splay.
Next, input a line with $$$n$$$ integers $$$a_1, a_2, \dots, a_n(1 \leq a_i \leq n)$$$, representing the cave numbers that Kangaroo Splay will probe next.
It is guaranteed that for all data in a test case, the sum of $$$n$$$ does not exceed $$$2 \times 10^5$$$.
Output a total of $$$T$$$ lines.
For each test case, if a feasible cave exists, output any one feasible cave number; if no such cave exists, output -1.
331 1 251 4 3 1 321 2
3 5 -1
