#include<iostream>
#include<algorithm>
#include<cstring>
using  namespace std;

const int N=510;
int n,m;
int g[N][N];
int dist[N];
bool st[N];
int dijstra()
{
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    for(int i=0;i<n-1;++i)
    {
        int t=-1;
        for(int k=1;k<=n;++k)
        {
            if(!st[k] && (t==-1 || dist[t]>dist[k]))
            {
                t=k;
            }
        }
       for(int j=1;j<=n;++j)
       {
           dist[j]=min(dist[j],dist[t]+g[t][j]);

       }
       st[t]=true;
    }
    if(dist[n]==0x3f3f3f3f) return -1;
    return dist[n];
}

int main()
{
    cin>>n>>m;
    memset(g,0x3f,sizeof g);
    while(m--)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        g[a][b]=min(g[a][b],c);
    }
    cout<<dijstra();
    return 0;
}