#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>
#include<queue>
#define maxn 50010
using namespace std;
int n,m,a,b,c,head[maxn],tot,dis[maxn];
struct Edge{
	int to,next,dis;
}edge[maxn<<1];
struct Node{
	int id,dist;
	Node(int a=0,int b=0)
	{
		id=a,dist=b;
	}
	bool operator <(const Node& x)const
	{
		return x.dist<dist;
	}
};
void Addedge(int x,int y,int z)
{
	edge[++tot].to=y;
	edge[tot].dis=z;
	edge[tot].next=head[x];
	head[x]=tot;
}
void Djs(int s)
{
	priority_queue<Node> q;
	memset(dis,0x7f,sizeof(dis));
	dis[s]=0;q.push(Node(s,0));
	while(!q.empty())
	{
		Node node=q.top();q.pop();
		s=node.id;
		if(dis[s]!=node.dist)continue;
		for(int i=head[s];i;i=edge[i].next)
		{
			int t=edge[i].to;
			if(dis[t]>dis[s]+edge[i].dis)
			{
				dis[t]=dis[s]+edge[i].dis;
				q.push(Node(t,dis[t]));
			}
		}
	}
}
int main(){
	freopen("longest.in","r",stdin);	freopen("longest.out","w",stdout);
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d%d",&a,&b,&c);
		Addedge(a,b,-c);
	}
	Djs(1);
//	cout<<dis[n]<<endl;
	if(dis[n]==0x7f7f7f7f)puts("-1");
	else printf("%d\n",-dis[n]);
}