write a go solution for Description:
You have n lamps, numbered from 1 to n. Initially, all the lamps are turned off.

You also have n buttons. The i-th button toggles all the lamps whose index is a multiple of i. When a lamp is toggled, if it was off it turns on, and if it was on it turns off.

You have to press some buttons according to the following rules.

- You have to press at least one button.
- You cannot press the same button multiple times.
- You are given m pairs (u_i,v_i). If you press the button u_i, you also have to press the button v_i (at any moment, not necessarily after pressing the button u_i). Note that, if you press the button v_i, you don't need to press the button u_i.

You don't want to waste too much electricity. Find a way to press buttons such that at the end at most lfloorn/5rfloor lamps are on, or print -1 if it is impossible.

Input Format:
Each test contains multiple test cases. The first line contains the number of test cases t (1<=t<=10^4). The description of the test cases follows.

The first line of each test case contains two integers n and m (1<=n<=2*10^5, 0<=m<=2*10^5) — the number of lamps and the number of pairs, respectively.

Each of the next m lines contains two integers u_i, v_i (1<=qu_i,v_i<=qn, u_ineqv_i). If you press the button u_i, you also have to press the button v_i. It is guaranteed that the pairs (u_i,v_i) are distinct.

It is guaranteed that the sum of n and the sum of m over all test cases do not exceed 2*10^5.

Output Format:
For each test case:

- If there is no choice of buttons that makes at most lfloorn/5rfloor lamps on at the end, output a single line containing -1.
- Otherwise, output two lines. The first line should contain an integer k (1<=k<=n) — the number of pressed buttons. The second line should contain k integers b_1,b_2,...,b_k (1<=b_i<=n) — the indices of the pressed buttons (in any order). The b_i must be distinct, and at the end at most lfloorn/5rfloor lamps must be turned on.

Note:
In the first test case, you need to turn at most lfloor4/5rfloor lamps on, which means that no lamp can be turned on. You can show that no choice of at least one button turns 0 lamps on.

In the second test case, you can press buttons 3, 5, 1, 2.

- Initially, all the lamps are off;
- after pressing button 3, the lamps whose index is a multiple of 3 (i.e., 3) are toggled, so lamp 3 is turned on;
- after pressing button 5, the lamps whose index is a multiple of 5 (i.e., 5) are toggled, so lamps 3, 5 are turned on;
- after pressing button 1, the lamps whose index is a multiple of 1 (i.e., 1, 2, 3, 4, 5) are toggled, so lamps 1, 2, 4 are turned on;
- after pressing button 2, the lamps whose index is a multiple of 2 (i.e., 2, 4) are toggled, so lamp 1 is turned on.

This is valid because

- you pressed at least one button;
- you pressed all the buttons at most once;
- you pressed button u_2=5, which means that you had to also press button v_2=1: in fact, button 1 has been pressed;
- at the end, only lamp 1 is on.

In the third test case, pressing the buttons 8, 9, 10 turns only the lamps 8, 9, 10 on.. Output only the code with no comments, explanation, or additional text.