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;
typedef long long ll;
const int MOD=1e9+7;
const int INF=1e9;
const ll LINF=1e18;

vector<ll> dijkstra(vector<vector<pair<int,int>>>& graph,int s){
    int n=(int)graph.size();
    priority_queue<pair<ll,int>,vector<pair<ll,int>>,greater<pair<ll,int>>> pq;
    vector<ll> dist(n,LINF);
    dist[s]=0;
    pq.push({0,s});
    while(pq.size()){
        auto p=pq.top();
        pq.pop();
        int v=p.second;
        if(dist[v]<p.first)continue;
        for(auto edge:graph[v]){
            int u=edge.first;
            int w=edge.second;
            if(dist[v]+w<dist[u]){
                dist[u]=dist[v]+w;
                pq.push({dist[u],u});
            }
        }
    }
    return dist;
}

int main(){
    int n,m;
    cin>>n>>m;
    vector<vector<pair<int,int>>> g(n);
    for(int i=0;i<n-1;i++){
        g[i+1].push_back({i,0});
    }
    for(int i=0;i<m;i++){
        int a,b,c;
        cin>>a>>b>>c;
        --a,--b;
        g[a].push_back({b,c});
    }
    vector<ll> d=dijkstra(g,0);
    cout<<(d[n-1]==LINF?-1:d[n-1])<<endl;
}