write a go solution for Description:
You are given n segments on a number line, numbered from 1 to n. The i-th segments covers all integer points from l_i to r_i and has a value w_i.

You are asked to select a subset of these segments (possibly, all of them). Once the subset is selected, it's possible to travel between two integer points if there exists a selected segment that covers both of them. A subset is good if it's possible to reach point m starting from point 1 in arbitrary number of moves.

The cost of the subset is the difference between the maximum and the minimum values of segments in it. Find the minimum cost of a good subset.

In every test there exists at least one good subset.

Input Format:
The first line contains two integers n and m (1<=n<=3*10^5; 2<=m<=10^6) — the number of segments and the number of integer points.

Each of the next n lines contains three integers l_i, r_i and w_i (1<=l_i<r_i<=m; 1<=w_i<=10^6) — the description of the i-th segment.

In every test there exists at least one good subset.

Output Format:
Print a single integer — the minimum cost of a good subset.

Note:
None. Output only the code with no comments, explanation, or additional text.