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<iomanip>
#include<cassert>
#include<math.h>
#include<complex>
#include<algorithm>
#include<utility>
#include<queue>
#include<string.h>
#include<string>
#include<set>
#include<map>
#include<unordered_map>
#include<functional>
#include<vector>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
const ll INF=2e18;
const ll MOD=1e9+7;

ll N,M;
struct Edge{ll to,cost;};
vector<Edge> edgeList[100010];
ll d[100010];
int main(){
    cin>>N>>M;
	for(ll i=0;i<M;i++){
		ll l,r,c;cin>>l>>r>>c;
		l--;r--;
		edgeList[l].push_back(Edge{r,c});
	}
	for(ll i=1;i<N;i++){
		edgeList[i].push_back(Edge{i-1,0});
		d[i]=INF;
	}
	d[0]=0;	
	priority_queue<P,vector<P>,greater<P>> pq;
	pq.push(P(0,0));
	while(!pq.empty()){
		ll now=pq.top().second;
		ll nowC=pq.top().first;pq.pop();
		if(nowC>d[now])continue;
		for(auto e:edgeList[now]){
			ll newC=nowC+e.cost;
			if(d[e.to]>newC){
				d[e.to]=newC;
				pq.push(P(newC,e.to));
			}
		}
	}
	cout<<((d[N-1]==INF)?(-1):d[N-1]);
    return 0;
}