Problem: We have N points numbered 1 to N arranged in a line in this order.

Takahashi decides to make an undirected graph, using these points as the vertices. In the beginning, the graph has no edge. Takahashi will do M operations to add edges in this graph. The i-th operation is as follows:

* The operation uses integers L_i and R_i between 1 and N (inclusive), and a positive integer C_i. For every pair of integers (s, t) such that L_i \leq s < t \leq R_i, add an edge of length C_i between Vertex s and Vertex t.



The integers L_1, ..., L_M, R_1, ..., R_M, C_1, ..., C_M are all given as input.

Takahashi wants to solve the shortest path problem in the final graph obtained. Find the length of the shortest path from Vertex 1 to Vertex N in the final graph.

Constraints

* 2 \leq N \leq 10^5
* 1 \leq M \leq 10^5
* 1 \leq L_i < R_i \leq N
* 1 \leq C_i \leq 10^9

Input

Input is given from Standard Input in the following format:


N M
L_1 R_1 C_1
:
L_M R_M C_M


Output

Print the length of the shortest path from Vertex 1 to Vertex N in the final graph. If there is no shortest path, print `-1` instead.

Examples

Input

4 3
1 3 2
2 4 3
1 4 6


Output

5


Input

4 2
1 2 1
3 4 2


Output

-1


Input

10 7
1 5 18
3 4 8
1 3 5
4 7 10
5 9 8
6 10 5
8 10 3


Output

28

Solution (in JAVA):

Solution:

import java.util.*;

public class Main {

    Edge[] g;
    int n;


    void run() {
        Scanner sc = new Scanner(System.in);

        n = sc.nextInt();
        int m = sc.nextInt();

        g = new Edge[n];
        for (int i = 0; i < n; i++) {
            g[i] = new Edge();
            if (i != 0) g[i].add(new P(i - 1, 0));
        }

        for (int i = 0; i < m; i++) {
            int l = sc.nextInt() - 1, r = sc.nextInt() - 1, c = sc.nextInt();
            g[l].add(new P(r, c));
        }
        System.out.println(dijkstra());
    }

    long dijkstra() {
        long[] d = new long[n];
        Arrays.fill(d, 1L << 60);
        d[0] = 0;
        PriorityQueue<P> q = new PriorityQueue<>(Comparator.comparingLong(p -> p.c));
        q.add(new P(0, 0));

        while (!q.isEmpty()) {
            P cur = q.remove();
            if (cur.t == n - 1) return cur.c;
            if (cur.c != d[cur.t]) continue;

            for (P next: g[cur.t]) {
                if (d[next.t] > cur.c + next.c) {
                    d[next.t] = cur.c + next.c;
                    q.add(new P(next.t, cur.c + next.c));
                }
            }
        }
        return -1;
    }

    class Edge extends ArrayList<P> {}

    class P {
        int t;
        long c;
        P(int t, long c) {
            this.t = t;
            this.c = c;
        }
    }

    void debug(Object...os) {
        System.err.println(Arrays.deepToString(os));
    }

    public static void main(String[] args) {
        new Main().run();
    }

}