#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>
#include <vector>
#define x first
#define y second

using namespace std;

typedef pair<int, int> PII;

const int N = 1e6+10;

int h[N], e[N], ne[N], w[N], idx;   //稠密图用邻接表
int dist[N];    
bool st[N];
int n, m;

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

int dijkstra()
{
    memset(dist, 0x3f, sizeof dist);    //初始化距离
    dist[1] = 0;    //初始化起点距离
    priority_queue<PII, vector<PII>, greater<PII> > heap;   //定义一个小根堆
    heap.push({0, 1});      //起点入堆

    while ( heap.size() )   //当堆不空的时候
    {
        PII t = heap.top();     //取堆顶
        heap.pop();     //弹出

        int ver = t.second;     //取出边
        if ( st[ver] ) continue;    //如果当前点已经更新过，跳过此次
        st[ver] = true;     //标记点的状态

        for ( int i = h[ver]; i != -1; i = ne[i] )      //遍历当前点能到达的点
        {
            int j = e[i];   //取出能到达的点
            if ( dist[j] > dist[ver] + w[i] )   //判断距离是否用跟新
            {
                dist[j] = dist[ver] + w[i]; 
                heap.push({dist[j], j});        //更新距离后入堆
            }
        }
    }
    if ( dist[n] == 0x3f3f3f3f ) return -1;
    return dist[n];
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    memset(h, -1, sizeof h);
    cin >> n >> m;
    while ( m -- )
    {
        int a, b, w;
        cin >> a >> b >> w;
        add(a, b, w);
    }

    int t = dijkstra();
    if ( t == -1 ) puts("-1");
    else cout << t << endl;
    return 0;
}