#include<bits/stdc++.h>
#define M 55001
using namespace std;
int n,m,s;
priority_queue<pair<int ,int> >q;
int dis[M],qnext[M],ver[M],tance[M],head[M],num;
int x,y,z;
void add(int fr,int to,int di)
{
	dis[++num]=di;
	ver[num]=to;
	qnext[num]=head[fr];
	head[fr]=num;
}
void D(int u)
{
	
	tance[u]=0;
	q.push(make_pair(0,u));
	while(!q.empty())
	{
		int cnt;
		cnt=q.top().second;
		q.pop();
		for(int i=head[cnt];i;i=qnext[i])
		{
		int y=ver[i],z=dis[i];
			if(tance[y]<tance[cnt]+z)
			tance[y]=tance[cnt]+z;
			q.push(make_pair(tance[y],y));
		}
	}
}
int main(){
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)
	tance[i]=-1;
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d%d",&x,&y,&z);
        add(x,y,z);
	}
    
    D(1);
    printf("%d",tance[n]);
	return 0;
}