样例输入：

5 12
1 5 5
3 4 10
4 10 6
11 12 5
10 12 3

样例输出

3

样例输入：

1 10
1 10 23

样例输出

0

#define mid ((l + r) >> 1)
int t[maxn], tg[maxn];
struct seg {
	int l, r, w;
	bool friend operator <(seg a, seg b){
		return a.w < b.w;
	}
} seg[maxn];
int n, m;
void Modify(int rt, int l, int r, int L, int R, int val)
{
	if (l >= L && r <= R) {
		t[rt] += val;
		tg[rt] += val;
		return;
	}
	if (L <= mid) Modify(rt << 1, l, mid, L, R, val);
	if (R > mid) Modify(rt << 1 | 1, mid + 1, r, L, R, val);
	t[rt] = tg[rt] + min(t[rt << 1], t[rt << 1 | 1]);
	return;
}
int main()
{
	n = read, m = read;
	for (int i = 1; i <= n; i++) {
		seg[i].l = read, seg[i].r = read, seg[i].w = read;
	}
	sort(seg + 1, seg + 1 + n);
	int l = 1, ans = 1 << 30;

	for (int r = 1; r <= n; r++) {
		Modify(1, 1, m - 1, seg[r].l, seg[r].r - 1, 1);
		while (t[1]) {
			ans = min(ans, seg[r].w - seg[l].w);
			Modify(1, 1, m - 1, seg[l].l, seg[l].r - 1, -1);
			l++;
		}
	}
	cout << ans << endl;
	return 0;
}
/**


 **/