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;
struct edge{long long to,cost;};
typedef pair<long long,int>P;
#define INF 1145141919810893
long long V;
vector<edge>G[10*10*10*10*10*5];
long long d[10*10*10*10*10*5];
void dijkstra(long long s){
	//greater<P>を指定することでfirstを小さい順に取り出せるようにする
	priority_queue<P,vector<P>,greater<P> >que;
	fill(d,d+V,INF);
	d[s]=0;
	que.push(P(0,s));
	while(!que.empty()){
		P p=que.top();
		que.pop();
		long long v=p.second;
		if(d[v]<p.first){
			continue;
		}
		for(long long i=0;i<G[v].size();i++){
			edge e=G[v][i];
			if(d[e.to]>d[v]+e.cost){
				d[e.to]=d[v]+e.cost;
				que.push(P(d[e.to],e.to));
			}
		}

	}
}
int main(){
	long long M;
	cin>>V>>M;
	for(long long i=0;i<M;i++){
		long long l,r,c;
		cin>>l>>r>>c;
		l--;
		r--;
		struct edge a;
		a.to=r;
		a.cost=c;
		G[l].push_back(a);
	}
	for(long long i=V-1;i>0;i--){
		long long l,r,c;
		struct edge x;
		x.to=i-1;
		x.cost=0;
		G[i].push_back(x);
	}
	dijkstra(0);
	if(d[V-1]==INF){
		d[V-1]=-1;
	}
	cout<<d[V-1]<<endl;

	
}