import java.util.*;

public class Main{
    public static int INF = 0x3f3f3f3f;
    public static int n;
    public static Map<Integer, List<Node>> map = new HashMap<>();
    public static int[] dist;
    public static boolean[] st;

    public static class Node {
        public int node;
        public int length;

        public Node(int node, int length) {
            this.node = node;
            this.length = length;
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        dist = new int[n + 1];
        st = new boolean[n + 1];
        for (int i = 1; i <= n ; i ++) {
            map.put(i, new ArrayList<>());

        }
        int m = sc.nextInt();
        for (int i = 0; i < m ; i ++ ) {
            int x = sc.nextInt();
            int y = sc.nextInt();
            int z = sc.nextInt();
            map.get(x).add(new Node(y, z));
        }
        int res = dijkstra();
        System.out.println(res);

    }

    public static int dijkstra() {
        for (int i = 1; i <= n ; i ++) {
            dist[i] = INF;
        }
        dist[1] = 0;
        for (int i = 0; i < n ; i ++ ) {
            int t = 0;
            for (int j = 1; j <= n; j ++ ) {
                if(!st[j] && (t == 0 || dist[t] > dist[j])) t = j;
            }
            st[t] = true;

            for (Node next : map.get(t)) {
                int j = next.node;
                int len = next.length;
                dist[j] = Math.min(dist[j], dist[t] + len);
            }

        }
        if(dist[n] == INF) {
            return -1;
        }
        return dist[n];
    }
}