inline void DFS (int x, int fa)
{
	for (int i = head[x]; ~ i; i = next[i])
	{
		if (key[i] == fa) continue;
		DFS (key[i], x);
		ans = max (ans, d[x] + len[i] + d[key[i]]);
		d[x] = max (d[x], d[key[i]] + len[i]);
	}
}