#include <iostream>
#include <cstring>
using namespace std;
const int N = 510;
int graph[N][N];
bool st[N];
int dist[N];
int n, m;
int dijkstra(){
    memset(dist, 0x3f3f3f, sizeof dist);
    dist[1] = 0;
    for(int i = 0; i < n; i ++ ){
        int nxt = -1;
        // 找到距离当前起点的最近的点
        for(int j = 1;j <= n; j ++ ){
            if(!st[j] && (nxt == -1 || dist[nxt] > dist[j]))    nxt = j;
        }
        st[nxt] = true;
        // 用nxt点去更新集合内的其他距离
        for(int j = 1; j <= n; j ++ ){
            if(dist[j] > dist[nxt] + graph[nxt][j]){
                dist[j] = dist[nxt] + graph[nxt][j];
            }
        }
    }
    if(dist[n] >= 0x3f3f3f)     return -1;
    return dist[n];
}

int main(){
    cin >> n >> m;
    memset(graph, 0x3f3f3f, sizeof graph);
    int x, y, z;
    for(int i = 0; i < m; i ++ ){
        cin >> x >> y >> z;
        graph[x][y] = min(graph[x][y], z);
    }
    cout << dijkstra() << endl;
    return 0;
}