write a go solution for Description:
Moamen was drawing a grid of n rows and 10^9 columns containing only digits 0 and 1. Ezzat noticed what Moamen was drawing and became interested in the minimum number of rows one needs to remove to make the grid beautiful.

A grid is beautiful if and only if for every two consecutive rows there is at least one column containing 1 in these two rows.

Ezzat will give you the number of rows n, and m segments of the grid that contain digits 1. Every segment is represented with three integers i, l, and r, where i represents the row number, and l and r represent the first and the last column of the segment in that row.

For example, if n=3, m=6, and the segments are (1,1,1), (1,7,8), (2,7,7), (2,15,15), (3,1,1), (3,15,15), then the grid is:

Your task is to tell Ezzat the minimum number of rows that should be removed to make the grid beautiful.

Input Format:
The first line contains two integers n and m (1<=n,m<=3*10^5).

Each of the next m lines contains three integers i, l, and r (1<=i<=n, 1<=l<=r<=10^9). Each of these m lines means that row number i contains digits 1 in columns from l to r, inclusive.

Note that the segments may overlap.

Output Format:
In the first line, print a single integer k — the minimum number of rows that should be removed.

In the second line print k distinct integers r_1,r_2,ldots,r_k, representing the rows that should be removed (1<=r_i<=n), in any order.

If there are multiple answers, print any.

Note:
In the first test case, the grid is the one explained in the problem statement. The grid has the following properties:

1. The 1-st row and the 2-nd row have a common 1 in the column 7.
2. The 2-nd row and the 3-rd row have a common 1 in the column 15.

In the second test case, the given grid is as follows:. Output only the code with no comments, explanation, or additional text.