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 CPP):

Solution:
#include <algorithm>
#include <iostream>
#include <vector>

using ll = long long;
using namespace std;

int main() {
    ll inf = 1e18;
    int n, m;
    cin >> n >> m;
    ll d[n];
    d[0] = 0;
    for (int i = 1; i < n; ++i) d[i] = inf;
    vector<vector<int>> a(m, vector<int>(3));
    for (int i = 0; i < m; ++i) {
        int l, r, c;
        cin >> l >> r >> c;
        a[i][0] = l-1;
        a[i][1] = r-1;
        a[i][2] = c;
    }
    sort(a.begin(), a.end());
    for (const auto& e : a) {
        int l = e[0], r = e[1], c = e[2];
        for (int j = l; j < r; ++j) {
            ll t = d[j] + c;
            if (t < d[r]) d[r] = t;
        }
    }
    if (d[n-1] == inf) cout << -1 << endl;
    else cout << d[n-1] << endl;
}