#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,int> PII;
const ll INF=LLONG_MAX;
const int N=1e5+10;
bool st[N];
ll dist[N];
struct edge{
    int v;
    ll w;
};
vector<edge> adj[N];
int n,m;
void Dijkstra(){
    fill(dist+1,dist+n+1,INF);
    priority_queue<PII,vector<PII>,greater<PII>>q;
    q.push({0,1});
    dist[1] = 0 ;
    while(!q.empty())
    {
        int u = q.top().second;q.pop();
        if(st[u]) continue;
        st[u] = true;
        for(int i = 0 ; i < adj[u].size();i++)
        {
            int v = adj[u][i].v;
            ll w = adj[u][i].w;
            if(dist[u] + w < dist[v])
            {
                
                dist[v] = dist[u] + w;
                
                q.push({dist[v],v});
            }
        }
        
        
    }
    
}
int main(){
    cin>>n>>m;
    for(int i=1;i<=m;i++){
        int u,v,w;
        cin>>u>>v>>w;
        adj[u].push_back({v,w});
    }
    Dijkstra();
    if(dist[n]==INF) cout<<-1;
    else cout<<dist[n];
    return 0;
}