#include<iostream>
#include<vector>
#include<deque>
#include<map>
using namespace std;
const int N=1505;
struct Node{
	int x;
	int y;
	bool operator<(const Node& other)const{
		if(x!=other.x)return x<other.x;
		return y<other.y;
	}
};
vector<int>side[N];
map<Node,int>length;
bool inQueue[N];
bool allVisit[N];
int maxSize[N];
int main(){
	int n,m;
	scanf("%d%d",&n,&m);
	for(int i=0;i<m;i++){
		int u,v,w;
		scanf("%d%d%d",&u,&v,&w);
		side[u].push_back(v);
		if(length[{u,v}])length[{u,v}]=max(length[{u,v}],w);
		else length[{u,v}]=w;
	}
	deque<int>bfs;
	bfs.push_back(1);
	inQueue[1]=true;
	while(!bfs.empty()){
		int head=bfs.front();
		bfs.pop_front();
		inQueue[head]=false;
		for(int i=0;i<side[head].size();i++){
			if(maxSize[side[head][i]]<maxSize[head]+length[{head,side[head][i]}]){
				maxSize[side[head][i]]=maxSize[head]+length[{head,side[head][i]}];
				if(!inQueue[side[head][i]]){
					bfs.push_back(side[head][i]);
					inQueue[side[head][i]]=true;
					allVisit[side[head][i]]=true;
				}
			}
		}
	}
	if(allVisit[n])printf("%d\n",maxSize[n]);
	else printf("-1\n");
	return 0;
}