#include<stdio.h>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
const int maxn=1510,maxe=100010;
struct Edge{
	int to,next,dis;
}e[maxe];

int n,m,len=0;
int head[maxn],dis[maxn];
bool vis[maxn];

void Insert(int x,int y,int z){
	len++;e[len].to=y;e[len].dis=z;e[len].next=head[x];head[x]=len;
}

void Spfa(int x){
	queue<int> q;
	q.push(x);vis[x]=1;
	while(!q.empty()){
		int k=q.front();q.pop();vis[k]=0;
		for(int i=head[k];i!=-1;i=e[i].next){
			int j=e[i].to;
			if(dis[j]<dis[k]+e[i].dis){
				dis[j]=dis[k]+e[i].dis;
				if(!vis[j]){
					vis[j]=1;
					q.push(j);
				}
			}
		}
	}
	if(dis[n]==0)printf("-1\n");
	else printf("%d",dis[n]);
}

int main()
{
	freopen("longest.in","r",stdin);
	freopen("longest.out","w",stdout);
	memset(head,-1,sizeof head);
	scanf("%d%d",&n,&m);int x,y,z;
	for(int i=1;i<=m;i++){
		scanf("%d%d%d",&x,&y,&z);
		Insert(x,y,z);
	}
	Spfa(1);
	return 0;
}