#include<iostream>
#include<cstring>
#include<algorithm>

using namespace std;
const int N=510;
int n,m;
int g[N][N];
int dist[N];
bool st[N];
int dijkstra()
{

    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    for(int i=0;i<n;i++)    
    {
        int t=-1;
        for(int j=1;j<=n;j++)
        if(!st[j]&&(t==-1||dist[t]>dist[j]))t=j;
        if(t==n)break;
        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);
       // printf("%d\n",g[a][b]);
    }
    printf("%d",dijkstra());
    return 0;
}