#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5e5 + 5;
struct Edge {
	int to, nxt, w;
} e[MAXN];
int h[MAXN], cnt;
void addedge(int u, int v, int w) {
	e[++cnt].to = v, e[cnt].nxt = h[u], e[cnt].w = w, h[u] = cnt;
}
int n, m;
typedef pair<int, int> pii;
priority_queue<pii, vector<pii>, greater<pii> > q;
int dis[MAXN], vis[MAXN];
void dijkstra() {
	memset(dis, 0x3f, sizeof(dis));
	dis[1] = 0;
	pii res = make_pair(0, 1);
	q.push(res);
	while (!q.empty()) {
		res = q.top(); q.pop();
		int dist = res.first, u = res.second;
		if (vis[u]) continue;
		vis[u] = 1;
		for (int i = h[u]; i; i = e[i].nxt) {
			int v = e[i].to;
			if (!vis[v] && dis[v] > dis[u] + e[i].w) {
				dis[v] = dis[u] + e[i].w;
				q.push(make_pair(dis[v], v));
			}
		}
	}
}
int main() {
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		int u, v, w;
		cin >> u >> v >> w;
		addedge(u, v, -w);
	}
	dijkstra();
	if (dis[n] >= 0x3f3f3f3f) cout << -1 << endl;
	else cout << -dis[n] << endl;
	return 0;
}