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 <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define Maxn 100000
#define ll long long
#define Inf 0x3f3f3f3f3f3f3f3fll
int head[Maxn+5],arrive[Maxn<<1|5],nxt[Maxn<<1|5],val[Maxn<<1|5],tot;
void add_edge(int from,int to,int w){
	arrive[++tot]=to;
	nxt[tot]=head[from];
	val[tot]=w;
	head[from]=tot;
}
ll dis[Maxn+5];
priority_queue<pair<int,int>,vector<pair<int,int> >,greater<pair<int,int> > > q;
bool vis[Maxn+5];
void dij(){
	memset(dis,0x3f,sizeof dis);
	dis[1]=0;
	q.push(make_pair(0,1));
	int u;
	while(!q.empty()){
		u=q.top().second;
		q.pop();
		if(vis[u]){
			continue;
		}
		vis[u]=1;
		for(int i=head[u];i;i=nxt[i]){
			int v=arrive[i];
			if(dis[u]+val[i]<dis[v]){
				dis[v]=dis[u]+val[i];
				q.push(make_pair(dis[v],v));
			}
		}
	}
}
int main(){
	int n,m;
	int l,r,c;
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++){
		scanf("%d%d%d",&l,&r,&c);
		add_edge(l,r,c);
	}
	for(int i=1;i<n;i++){
		add_edge(i+1,i,0);
	}
	dij();
	cout<<(dis[n]==Inf?-1:dis[n])<<endl;
	return 0;
}