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;
#ifdef LOCAL_DEBUG
  #include "LOCAL_DEBUG.hpp"
#endif
#define int long long
const int INF = 1LL << 60;

struct edge{ int to,cost; };
vector<int> dikstra(int s,vector<vector<edge>> G){
  typedef pair<int, int> P;
  const int INF = 1LL << 60;

  priority_queue<P,vector<P>,greater<P>> que;
  vector<int> d(G.size(),INF); //sからの最短距離
  d[s] = 0;
  que.push({0,s}); //{最短距離,頂点}

  while( !que.empty() ){
    P p = que.top(); que.pop();
    int v = p.second;
    if(d[v] < p.first) continue;
    for(auto e : G[v]){
      if(d[e.to] > d[v] + e.cost){
        d[e.to] = d[v] + e.cost;
        que.push( {d[e.to],e.to} );
      }
    }
  }
  return d;
}

signed main(){

  int n, m; cin >> n >> m;
  vector<vector<edge>> G(n);
  for(int i = 0; i < m; i++){
    int l, r, c; cin >> l >> r >> c;
    l--, r--;
    G[l].push_back({r,c});
  }
  for(int i = 1; i < n; i++){
    G[i].push_back({i-1, 0});
  }
  auto dp = dikstra(0, G);
  cout << (dp[n-1] == INF ? -1 : dp[n-1]) << endl;

  return 0;
}