#include <bits/stdc++.h>
using namespace std;
int n,m,in[2005],maxa[2005];bool vis[2005];
struct node{
	int to,w;
};
vector <node> G[2005];
queue <int> q;
void topo(){
	memset(maxa,0x3f,sizeof(maxa));
	maxa[1] = 0,maxa[n] = -1;
	for (int i = 1;i <= n;i++) if (!in[i]) q.push(i);
	while (!q.empty()){
		int u = q.front();
		for (int i = 0;i < G[u].size();i++){
			int v = G[u][i].to;
			maxa[v] = max(maxa[v],maxa[u]+G[u][i].w);
			in[v]--;
			if (!in[v]) q.push(v);
		}
		q.pop(); 
	}
}
int main(){
	cin >> n >> m;
	int u,v,w;
	while (m--){
		cin >> u >> v >> w;
		G[u].push_back(node{v,w});
		in[v]++;
	}
	topo();
	cout << maxa[n];
	return 0;
}