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 {

    public static void main(String[] args) {
        final Scanner scanner = new Scanner(System.in);
        solve(scanner);
    }

    // int N = scanner.nextInt();
    // scanner.nextLine();
    // int[] n = Arrays.stream(scanner.nextLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    static void solve(Scanner scanner) {
        int N = scanner.nextInt(), M = scanner.nextInt();
        scanner.nextLine();
        List<List<Edge>> edgeList = new ArrayList<>();
        for (int i = 0; i < N; i++) {
            edgeList.add(new ArrayList<>());
            if (i > 0) {
                edgeList.get(i).add(new Edge(i - 1, 0));
            }
        }
        for (int i = 0; i < M; i++) {
            int[] e = Arrays.stream(scanner.nextLine().split(" ")).mapToInt(Integer::parseInt).toArray();
            edgeList.get(e[0] - 1).add(new Edge(e[1] - 1, e[2]));
        }

        Queue<Edge> q = new PriorityQueue<>(Comparator.comparingLong(x -> x.cost));
        q.add(new Edge(0, 0));
        long dist[] = new long[N];
        Arrays.fill(dist, Long.MAX_VALUE / 2);
        while (!q.isEmpty()) {
            Edge e = q.poll();
            if (dist[e.to] <= e.cost) {
                continue;
            }
            dist[e.to] = e.cost;
            for (Edge ne: edgeList.get(e.to)) {
                q.add(new Edge(ne.to, e.cost + ne.cost));
            }
        }
        System.out.println(dist[N - 1] == Long.MAX_VALUE / 2 ? -1 : dist[N - 1]);
    }

    static class Edge {
        int to;
        long cost;

        public Edge(int to, long cost) {
            this.to = to;
            this.cost = cost;
        }
    }
}