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.Arrays;
import java.util.Scanner;
import java.util.TreeSet;

class D {
    public static void main(String... args) {
        final Scanner sc = new Scanner(System.in);
        final int N = sc.nextInt();
        final int M = sc.nextInt();
        final Segment[] segs = new Segment[M];
        for (int i = 0; i < M; i++)
            segs[i] = new Segment(i, sc.nextInt(), sc.nextInt(), sc.nextInt());
        final TreeSet<Segment> que = new TreeSet<>((Segment o1, Segment o2) -> o1.L == o2.L ? o1.idx - o2.idx : o1.L - o2.L);
        que.addAll(Arrays.asList(segs));
        final long[] dist = new long[N + 1];
        Arrays.fill(dist, Long.MAX_VALUE / 2);
        dist[1] = 0;
        final TreeSet<Segment> set = new TreeSet<>((Segment o1, Segment o2) ->
                o1.dist(dist) == o2.dist(dist) ? o1.idx - o2.idx : Long.compare(o1.dist(dist), o2.dist(dist)));
        for (int i = 1; i <= N; i++) {
            while (!set.isEmpty() && set.first().R < i)
                set.pollFirst();
            if (!set.isEmpty())
                dist[i] = set.first().dist(dist);
            while (!que.isEmpty() && que.first().L == i) {
                set.add(que.pollFirst());
            }
        }
        System.out.println(dist[N] < Long.MAX_VALUE / 2 ? dist[N] : -1);
    }

    static class Segment {
        final int idx, L, R, C;

        public Segment(int i, int l, int r, int c) {
            idx = i;
            L = l;
            R = r;
            C = c;
        }

        public long dist(final long[] dist) {
            return dist[L] + C;
        }
    }
}
public class Main {
    public static void main(String...args) {
        D.main();
    }
}