#include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
using namespace std;
queue<int>q;
int vis[1501]={0};
int dis[1501]={0};
vector<int>A[1501];
vector<int>C[1501];
int main(){
	freopen("longest.in","r",stdin);
	freopen("longest.out","w",stdout);
	int n,m;
	cin>>n>>m;
	int x,y,z;
	for(int i=1;i<=m;i++){
		cin>>x>>y>>z;
		A[x].push_back(y);
		C[x].push_back(z);
	}
	dis[1]=0;
	vis[1]=1;
	q.push(1);
	while(!q.empty()){
		int cd=q.front();
		q.pop();
		vis[cd]=0;
		for(int i=0;i<A[cd].size();i++){
			int u=A[cd][i];
			if(dis[u]<dis[cd]+C[cd][i]){
				dis[u]=dis[cd]+C[cd][i];
				if(!vis[u]){
					vis[u]=1;
					q.push(u);
				}
			}
		}
	}
	if(!dis[n])
		cout<<-1<<endl;
	else cout<<dis[n]<<endl;
return 0;
}