#include<bits/stdc++.h>
using namespace std;
struct{
	int begin;
	int end;
	int add;	
}a[1500002];
int ans,step,n,m,b[100000],t;
void bfs(int x,int step){
	if(x==n)ans=max(ans,step);
	for(int i=1;i<=n;i++){
		if(a[i].begin==x&&a[i].end!=0){
			t=a[i].end,a[i].end=0;
			bfs(t,step+a[i].add);
			a[i].end=b[i];
		}
	}
}
int main()
{
	cin>>n>>m;
	for(int i=1;i<=m;i++){
		int x,y,z;
		cin>>x>>y>>z,a[i].begin=x;
		a[i].end=y,a[i].add=z;
		b[i]=a[i].end;
	}
	bfs(1,step);
	if(ans!=0)cout<<ans<<endl;
	else cout<<"-1"<<endl;
}