#include <bits/stdc++.h>

using namespace std;

const int N = 2e5+10 , M = 2e5+10 , INF = 0x3f3f3f3f;

int n , m;
struct edge{
    int to , w;
};

struct node{
    int id , dis;
    bool operator < (const node &u) const{return dis > u.dis ;}
};

vector <edge> g[N];
int d[N];
bool vis[N];

void Dijkstra(int s)
{
    memset(d , INF , sizeof(d));
    d[s] = 0;
    priority_queue<node>q;
    q.push({s , d[s]});
    while(!q.empty())
    {
        node t = q.top();
        q.pop();
        int id = t.id , dis = t.dis;
        if(vis[id]) continue;
        vis[id] = true;
        for(int i = 0; i < g[id].size() ; i++)
        {
            edge e = g[id][i];
            if(vis[e.to]) continue;
            if(d[e.to] > d[id] + e.w)
            {
                d[e.to] = d[id] + e.w;
                q.push({e.to , d[e.to]});
            }

        }

    }

}


int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int u , v , w; cin >> u >> v >> w;
        g[u].push_back({v , w});
    }
    Dijkstra(1);
    if(d[n] != INF) cout << d[n];
    else cout << -1 ;

    return 0;
}