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

using namespace std;

const int N = 150000;
int h[N], w[N], e[N], ne[N], idx, m, n, dist[N], st[N];
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> q;

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

int dijstra()
{
    dist[1] = 0;
    q.push({0, 1});

    while (q.size())
    {
        auto t = q.top();
        q.pop();

        int ver = t.second, distance = t.first;
        if (st[ver]) continue;
        st[ver] = 1;

        for (auto i = h[ver]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > distance + w[i])
                {
                    dist[j] = distance + w[i];
                }
            q.push({dist[j], j});
        }
    }
    if(dist[m] == 0x3f3f3f3f) return -1;
    return dist[m];

}

int main()
{
    memset(dist, 0x3f, sizeof dist);
    memset(h, -1, sizeof h);
    cin >> m >> n;
    int a, b, c;
    while (n --)
    {
        cin >> a >> b >> c;
        add(a, b, c);
    }
    cout << dijstra() << endl;
    return 0;
}