rt,die码：

// # pragma GCC optimize("Ofast,no-stack-protector")

// # pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

# include <bits/stdc++.h>

using namespace std;

typedef long long ll;

typedef pair <int, int> pii;

int n, m, x, y, z, dis[30005];

vector <pii> v[30005];

bitset <30005> vis;

queue <int> q;

int main () {

	ios::sync_with_stdio (0);

	cin.tie (0);

	cout.tie (0);

	cin >> n >> m;

	v[0].push_back ({1, 0});

	for (int i = 1; i < n; ++ i)
		v[i].push_back ({i + 1, 0}), v[i + 1].push_back ({i, -1});

	while (m --) {

		cin >> x >> y >> z;

		v[x - 1].push_back ({y, z});

	}

	q.push (0);

	while (! q.empty ()) {

		x = q.front ();

		q.pop ();
//		cerr << x << ':' << dis[x] << '\n';
		vis[x] = 0;

		for (pii& i : v[x])
			if (i.second + dis[x] > dis[i.first]) {

				dis[i.first] = dis[x] + i.second;

				if (! vis[i.first])
					q.push (i.first), vis[i.first] = 1;

			}

	}
//	for (int i = 1; i < n; ++ i) cout << dis[i] << ' ';
	cout << dis[n];

	return 0;

}