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;
#define int long long
typedef vector<int> vi;
typedef pair<int,int> ii;
typedef vector<ii> vii;
vi dist;
vector<vii> AdjList;
const int inf=1e18+7;
void dijkstra(int s) {
    dist[s]=0;
    priority_queue<ii,vii,greater<ii>> pq;
    pq.push(ii(0,s));
    while (!pq.empty()) {
    ii front=pq.top();
	pq.pop();
    int d=front.first;
	int u=front.second;
    if(d==dist[u]) {
        for(int j=0 ; j<(int)AdjList[u].size() ; j++) {
            ii v=AdjList[u][j];
            if(dist[u]+v.second<dist[v.first]) {
                dist[v.first]=dist[u]+v.second;
                pq.push(ii(dist[v.first],v.first));
                }
            }
        }
    }
}
signed main() {
	int n,m;
	cin>>n>>m;
	AdjList.assign(n,vii());
	dist.assign(n,inf);
	for(int i=1 ; i<n ; i++) {
		AdjList[i].push_back(ii(i-1,0));
	}
	for(int i=0 ; i<m ; i++) {
		int u,v,w;
		cin>>u>>v>>w;
		u--; v--;
		AdjList[u].push_back(ii(v,w));
	}
	dijkstra(0);
	if(dist[n-1]==inf) cout<<-1;
	else cout<<dist[n-1];
}