#include<cstdio>
#include<cmath>
#include<iostream>
#include<cstring>
#include<queue>
#include<stack>
#include<algorithm>
using namespace std;
const int maxn=1550;
const int maxe=50005;
struct Edge{
	int to,dis,next;
}e[maxe];
int n,m,head[maxn],len=0,d[maxn];
void Init();
void Spfa(int);
void Insert(int,int,int);
int main(){
	freopen("longest.in","r",stdin);
	freopen("longest.out","w",stdout);
	Init();
	return 0;
}
void Init()
{
/*	memset(head,-1,sizeof(head));
	memset(d,0x7f,sizeof(d));
	memset(e,0,sizeof(e));*/
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++)
	{
		int x,y,z;
		scanf("%d%d%d",&x,&y,&z);
		Insert(x,y,z);
	}
	if(m)Spfa(1);
	if(d[n]==0)printf("-1\n");
	else printf("%d\n",d[n]);
}
void Insert(int x,int y,int z)
{
	len++;
	e[len].to=y;
	e[len].next=head[x];
	e[len].dis=z;
	head[x]=len;
}
void Spfa(int x)
{
	queue<int> q;
	bool f[maxn]={0};
	f[x]=1;d[x]=0;
	q.push(x);
	while(!q.empty())
	{
		int k=q.front();q.pop();f[k]=0;
		for(int i=head[k];i;i=e[i].next)
		{
			int j=e[i].to;
			if(d[j]<d[k]+e[i].dis)
			{
				d[j]=d[k]+e[i].dis;
				if(!f[j])
				{
					q.push(j);f[j]=1;
				}
			}
		}
	}
}