#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
int read()
{
	int x,f=1;
	char ch;
	while(ch=getchar(),!isdigit(ch))if(ch=='-')f=-1;
	x=ch-48;
	while(ch=getchar(),isdigit(ch))x=x*10+ch-48;
	return x*f;
}
void write(int x)
{
	if(x<0)x=-x,putchar('-');
	int cnt=0;char ch[50];
	while(ch[++cnt]=x%10+48,x/=10);
	while(putchar(ch[cnt]),--cnt);
	putchar('\n');
}
#define maxe 50100
#define maxn 1600
#define k a[i].t
struct edge
{
	int t,n,d;
}a[maxe];
int n,m,len,head[maxn],dis[maxn];
void insert(int x,int y,int z)
{
	a[++len].t=y;a[len].d=z;a[len].n=head[x];head[x]=len;
}
void spfa()
{
	memset(dis,-0x7f,sizeof dis);
	queue<int> q;
	q.push(1);
	dis[1]=0;
	while(!q.empty())
	{
		int x=q.front();q.pop();
		for(int i=head[x];i;i=a[i].n)
		{
			if(dis[k]<dis[x]+a[i].d)
			{
				dis[k]=dis[x]+a[i].d;
				q.push(k);
			}
		}
	}
	write(max(dis[n],-1));
}
int main()
{
	freopen("longest.in","r",stdin);
	freopen("longest.out","w",stdout);
	n=read(),m=read();
	for(int i=1;i<=m;i++)
	{
		int x=read(),y=read(),z=read();
		insert(x,y,z);
	}
	spfa();
	//system("pause");
//	fclose(stdin);
//	fclose(stdout);
}