import java.io.*;
import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.Queue;

class Main {

    static final int INF = Integer.MAX_VALUE / 2;

    //邻接表存储图
    static int idx;
    static int[] h = new int[200010];
    static int[] e = new int[200010];
    static int[] ne = new int[200010];
    static int[] w = new int[200010];

    static int n, m;
    static boolean[] visited = new boolean[200010];
    static int[] dist = new int[200010];

    static {
        Arrays.fill(dist, INF);
        Arrays.fill(h, -1);
    }

    static class MinDist implements Comparable<MinDist> {
        int e, d;

        public MinDist(int e, int d) {
            this.e = e;
            this.d = d;
        }

        @Override
        public int compareTo(MinDist o) {
            return this.d - o.d;
        }
    }

    static Queue<MinDist> heap = new PriorityQueue<>();

    static void insert(int a, int b, int v) {
        e[idx] = b;
        ne[idx] = h[a];
        w[idx] = v;
        h[a] = idx++;
    }

    static int dijkstra() {
        dist[1] = 0;
        heap.add(new MinDist(1,0));
        while (!heap.isEmpty()) {
            MinDist next = heap.poll();
            if (visited[next.e]) continue;
            visited[next.e] = true;
            for (int i = h[next.e]; i !=-1 ; i=ne[i]) {
                int point = e[i];
                int distance = w[i];
                if (dist[point]>dist[next.e]+distance) {
                    dist[point] = dist[next.e]+distance;
                    heap.add(new MinDist(point,dist[point]));
                }
            }
        }
        if (dist[n]!=INF) return dist[n];
        else return -1;
    }

    public static void main(String[] args) throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader in = new BufferedReader(isr);
        String[] strs = in.readLine().split(" ");
        n = Integer.parseInt(strs[0]);
        m = Integer.parseInt(strs[1]);
        for (int i = 0; i < m; i++) {
            strs = in.readLine().split(" ");
            int a = Integer.parseInt(strs[0]);
            int b = Integer.parseInt(strs[1]);
            int v = Integer.parseInt(strs[2]);
            insert(a, b, v);
        }

        System.out.println(dijkstra());

        in.close();
        isr.close();
    }
}