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;
#define int long long
#define pie 3.141592653589793238462643383279
#define mod 1000000007
#define INF LLONG_MAX/5
#define all(v) v.begin(),v.end()
#define P pair<int,int>
#define S second
#define F first
#define f(i,n) for(int i=0;i<n;i++)
pair<P,int> p[100000];
int x[100000];
priority_queue<P,vector<P>,greater<P>> q;
signed main(){
	int n,m,z=1,zz=0;
	cin>>n>>m;
	f(i,n){
		if(i)x[i]=INF;
	}
	f(i,m){
		cin>>p[i].F.F>>p[i].F.S>>p[i].S;
		p[i].F.S--;
		p[i].F.F--;
	}
	sort(p,p+m);
	while(z<n){
		for(;zz<m&&p[zz].F.F<z;zz++){
			q.push(P(p[zz].S+x[p[zz].F.F],zz));
		}
		if(q.empty()){
			puts("-1");
			return 0;
		}
		P pa=q.top();
		q.pop();
		for(;z<=p[pa.S].F.S;z++){
			x[z]=pa.F;
		}
	}
	cout<<x[n-1]<<endl;
}