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.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Arrays;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int n = Integer.parseInt(sa[0]);
		int m = Integer.parseInt(sa[1]);
		Hen[] arr = new Hen[m];
		for (int i = 0; i < m; i++) {
			sa = br.readLine().split(" ");
			Hen h = new Hen();
			h.l = Integer.parseInt(sa[0]) - 1;
			h.r = Integer.parseInt(sa[1]) - 1;
			h.c = Integer.parseInt(sa[2]);
			arr[i] = h;
		}
		br.close();

		Arrays.parallelSort(arr);

		long[] d = new long[n];
		Arrays.fill(d, Long.MAX_VALUE);
		d[0] = 0;
		for (int i = 0; i < m; i++) {
			Hen h = arr[i];
			if (d[h.l] == Long.MAX_VALUE) {
				System.out.println(-1);
				return;
			}
			long alt = d[h.l] + h.c;
			for (int j = h.r; j > h.l; j--) {
				if (d[j] <= alt) {
					break;
				}
				d[j] = alt;
			}
		}
		if (d[n - 1] == Long.MAX_VALUE) {
			System.out.println(-1);
		} else {
			System.out.println(d[n - 1]);
		}
	}

	static class Hen implements Comparable<Hen> {
		int l, r, c;

		@Override
		public int compareTo(Hen o) {
			if (l != o.l) {
				return l - o.l;
			}
			if (c != o.c) {
				return c - o.c;
			}
			return r - o.r;
		}
	}
}