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<queue>
#include<cstring>
#include<vector>

using namespace std;
typedef long long ll;
const int N = 1e6+5,M=N*2;
ll h[N],st[N],dist[N],cnt,n,m;
const ll inf = 0x3f3f3f3f3f3f3f3f;
struct node {
	ll to,nxt,w;
}eg[M*2];
void add(ll u,ll v,ll w){
	eg[cnt].w=w;eg[cnt].to=v;eg[cnt].nxt=h[u];h[u]=cnt++;
}
priority_queue<ll,vector<ll>,greater<ll> >q;
ll dijkstra(ll u){
	memset(st,0,sizeof(st));
//	memset(dist,0x3f,sizeof(dist));
	for(ll i=1;i<=n;i++) dist[i]=inf;
	dist[u]=0;
	q.push(u);
	while(!q.empty()){
		ll u=q.top();
		q.pop();
// 		if(st[u]) continue;
// 		st[u]=1;
		for(ll i=h[u];i!=-1;i=eg[i].nxt){
			ll v = eg[i].to;
//			if(st[v]) continue;
			if(dist[v]>dist[u]+eg[i].w){
				dist[v]=dist[u]+eg[i].w;
				q.push(v);
			} 
		}
	}
	if(dist[n]==inf) return -1;
	return dist[n];
}

int main(){
	memset(h,-1,sizeof(h));
	cnt=0;
	cin>>n>>m;
	for(ll i=1;i<=n;i++) add(i,i-1,0);
	for(ll i=0;i<m;i++){
		ll u,v,w;
		cin>>u>>v>>w;
		add(u,v,w);
	}
	cout<<dijkstra(1)<<endl;
	
	return 0;
}