#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<ctime>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<iomanip>
#include<functional>
#define JW fclose(stdin); fclose(stdout);
#define WJ(name) freopen(#name".in","r",stdin); freopen(#name".out","w",stdout);
using namespace std;
const int maxn=1510;
int head[maxn],tot=0,dis[maxn]={0};
struct Node{
	int bianhao,juli;
	Node(int x=0,int y=0){bianhao=x;juli=y;}
	bool operator <(const Node & a)const{return juli>a.juli;}
};
struct edges{
	int to,w,next;
};edges edge[50010];
template<typename T>inline void QR(T& x){
	char ch;bool f=0;
	while(ch=getchar(),(ch<'0'||ch>'9')&&ch!='-');
	if(ch=='-')f=1,ch=getchar();x=ch-48;
	while(ch=getchar(),ch>='0'&&ch<='9')x=x*10+ch-48;if(f)x=-x;
}
template<typename T>inline void QW(T _num){
	if(_num<0)putchar('-'),_num=-_num;
	short _cnt=0;char _str[30];
	while(_str[++_cnt]=_num%10+48,_num/=10);
	while(putchar(_str[_cnt]),--_cnt);
}
inline void addedge(int from,int to,int w){
	edge[++tot].to=to;
	edge[tot].w=w;
	edge[tot].next=head[from];
	head[from]=tot;
}
Node a;priority_queue<Node>que;
inline void djs(int s){
	dis[s]=0;
	que.push(Node(s,0));
	while(!que.empty()){
		if(a=que.top(),que.pop(),dis[a.bianhao]!=a.juli)continue;
		for(int i=head[a.bianhao];i!=-1;i=edge[i].next)
			if(dis[edge[i].to]<dis[a.bianhao]+edge[i].w){
				dis[edge[i].to]=dis[a.bianhao]+edge[i].w;
				que.push(Node(edge[i].to,dis[edge[i].to]));
			}
	}
}
int main(){
	WJ(longest);
	memset(head,-1,sizeof(head));
	int m,n,a,b,c;
	QR(n),QR(m);
	while(m--){
		QR(a),QR(b),QR(c);
		addedge(a,b,c);
	}
	djs(1);
	if(!dis[n])puts("-1");
	else QW(dis[n]);
	JW;
	return 0;
}