#include <iostream>
#include <cstring>
#include <queue>

#define PII pair<int,int>
using namespace std;

const int N = 2e5;
int m,n;
int ne[N],e[N],idx;
int h[N];
int w[N];
int ds[N];
bool k[N];

void add(int a,int b,int c){
    e[idx] = b;
    ne[idx] = h[a];
    w[idx] = c;
    h[a] = idx ++;
}

int dis(){
    memset(ds,0x3f,sizeof ds);
    ds[1] = 0;
    priority_queue<PII,vector<PII>,greater<PII>> hh;
    hh.push({0,1});
    while(hh.size()){
        auto gg = hh.top();
        hh.pop();
        int aa = gg.first;
        int bb = gg.second;
        if(k[bb] == true) continue;
        k[bb] = true;
        for(int i = h[bb]; i != -1; i = ne[i]){
            int ks = e[i];
            if(ds[ks] > aa + w[i]){
                ds[ks] = aa + w[i];
                hh.push({ds[ks],ks});
            }
        }
    }
    if(ds[n] >= 0x3f3f3f) return -1;
    else return ds[n];
}

int main(){
    cin >> n >> m;
    memset(h,-1,sizeof h);
    for(int i = 1; i <= m; i ++){
        int a,b,c;
        cin >> a >> b >> c;
        add(a,b,c);
    }
    cout << dis() << endl;
    return 0;
}