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 <iostream>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <string>
#include <cmath>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
struct edge{ll to,cost;};
int V,E;
const ll INF =1234567890123456;
vector<edge>g[100005];
ll d[100005];

void dijkstra(int s){
	priority_queue<P, vector<P>, greater<P>> que;
	fill(d, d + V+3, INF);
	d[s] = 0;
	que.push(P(0, s));
	while(!que.empty()){
		P p = que.top();
		que.pop();
		ll v = p.second;
		if(d[v] < p.first) continue;
		for(int 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));
			}
		}
	}
	return;
}
int main(){
	cin>>V>>E;
	for(int i=0;i<E;i++){
		ll a,b,c;
		cin>>a>>b>>c;
		g[a].push_back(edge{b,c});
	}
  for(int i=1;i<V;i++){
    g[i+1].push_back(edge{i,0});
  }
	dijkstra(1);
	if(d[V]==INF)cout<<-1<<endl;
	else cout<<d[V]<<endl;
}