#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <string>
#include <set>
#include <vector>
#include <algorithm>
using namespace std;
vector <int> v[1501],w[1501];
int a,b,c,d,l,m,n,s,p[10000000],r[1501],h=1,t;
bool bo[1501];
void SPFA(void)
{
    p[0]=1;
    r[1]=0;
    while (h>t)
    {
        bo[p[t]]=false;
        for (d=0;d<v[p[t]].size();d++)
            if (r[p[t]]+w[p[t]][d]>r[v[p[t]][d]])
            {
                r[v[p[t]][d]]=r[p[t]]+w[p[t]][d];
                if (bo[v[p[t]][d]]==false) 
                {
                    bo[v[p[t]][d]]=true;
                    p[h]=v[p[t]][d];
                    h++;
                }
            }
        t++;
    }
}
int main(void)
{
	freopen ("longest.in","r",stdin);
	freopen ("longest.out","w",stdout);
	scanf("%d%d",&a,&b);
	if (b==0)
	{
		printf("-1");
		return 0;
	}
	for (c=0;c<b;c++)
	{
		scanf("%d%d%d",&l,&m,&n);
		v[l].push_back(m);
		w[l].push_back(n);
	}
	SPFA();
	s=r[a];
	if (s==0) s=-1;
	printf("%d",s);
	fclose(stdin);
	fclose(stdout);
	return 0;
}