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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

import java.util.*;

public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Scanner sc = new Scanner(System.in);
        int V = Integer.parseInt(sc.next());
        int E = Integer.parseInt(sc.next());
        ArrayList<ArrayList<int[]>> edge = new ArrayList<ArrayList<int[]>>();
        for (int i=0;i<V;i++) {
            ArrayList<int[]> add = new ArrayList<int[]>();
            edge.add(add);
        }
        for (int i=0;i<E;i++) {
            int s = Integer.parseInt(sc.next())-1;
            int t = Integer.parseInt(sc.next())-1;
            int d = Integer.parseInt(sc.next());
            int[] add = {t, d};
            edge.get(s).add(add);
        }
        for (int i=1;i<V;i++) {
            int[] add = {i-1, 0};
            edge.get(i).add(add);
        }
        Comparator<long[]> comparator = new Comparator<long[]>() {
            @Override
            public int compare(long[] o1, long[] o2) {
                return Long.compare(o1[1], o2[1]);
            }
        };
        long[] ans = new long[V];
        for (int i=0;i<V;i++) {
            ans[i] = -1;
        }
        PriorityQueue<long[]> queue = new PriorityQueue<long[]>(comparator);
        int[] flag = new int[V];
        long[] first = {0, 0};
        queue.add(first);
        while(!queue.isEmpty()) {
            long[] rem = queue.remove();
            if (flag[(int)rem[0]]==1) {
                continue;
            }
            flag[(int)rem[0]]=1;
            ans[(int)rem[0]] = rem[1];
            // System.out.println("rem: " + Arrays.toString(rem));
            for (int[] tmp : edge.get((int)rem[0])) {
                long[] add = {tmp[0], tmp[1]+rem[1]};
                queue.add(add);
            }
        }
            if (ans[V-1]==-1) {
                System.out.println(-1);
            } else {
                System.out.println(ans[V-1]);
            }
        out.close();
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
}