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(int i=0;i<m;++i){
    int l=a[i][0],r=a[i][1],c=a[i][2];
    for(int j=l;j<r;++j){
      ll t=d[j]+c;
      if(t<d[r])d[r]=t;
    }
  }
  cout<<(d[n-1]==inf?-1:d[n-1])<<'\n';
}