#include<iostream>
#include<cstdio>
using namespace std;
int n,m,ni[1501][1501]={0},ans=-1;
int dfs(int x,int y);
int main()
{
	freopen("longest.in","r",stdin);
	freopen("longest.out","w",stdout);
	cin>>n>>m;
	if(m==0)
	{
		cout<<-1;
		return 0;
	}
	for(int i=0;i<m;i++)
	{
		int a,b,v;
		cin>>a>>b>>v;
		ni[a][b]=v;
	}
	dfs(1,0);
	cout<<ans;
}
int dfs(int x,int y)
{
	if(x==n)
	{
		if(y>ans)
		{
			ans=y;
		}
	}
	else
	{
	    for(int i=x+1;i<=n;i++)
	    {
		    if(ni[x][i]!=0)
			{
				dfs(i,y+ni[x][i]);
			}
		}
	}
}