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 <bits/stdc++.h>
using namespace std;

typedef long long ll;

ll N, M;
vector<tuple<ll, ll, ll>> E;
typedef pair<ll, ll> P;

ll solve() {
  ll v = 0, d = 0, e = 0;
  priority_queue<P, vector<P>, greater<P>> que;
  while (v != N - 1) {
    for (; e < E.size() && get<0>(E[e]) <= v; ++e) {
      ll l, r, c;
      tie(l, r, c) = E[e];
      que.push(make_pair(d + c, r));
    }
    if (que.empty()) return -1;
    ll dx, r;
    tie(dx, r) = que.top();
    que.pop();
    d = dx;
    v = r;
  }
  return d;
}
int main() {
  cin >> N >> M;
  for (ll i = 0; i < M; ++i) {
    ll l, r, c;
    cin >> l >> r >> c;
    --l;
    --r;
    E.push_back(make_tuple(l, r, c));
  }
  sort(E.begin(), E.end());
  cout << solve() << endl;
  return 0;
}