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 int ll;
typedef pair<ll,int> li;
typedef pair<int,ll> il;
typedef vector<il> vil;
typedef vector<int> vi;
typedef pair<int,int> ii;
typedef vector<ii> vii;
vector<vil> graph;
vector<ll> dist;
void dijkstra()
{
	dist[1] = 0ll;
	priority_queue<li,vector<li>,greater<li> >pq;
	pq.push(li(0ll,1));
	while(!pq.empty())
	{
		li x = pq.top();pq.pop();
		ll a = x.first;
		int b = x.second;
		if(dist[b]==a)
		{
			for(int i=0;i<graph[b].size();++i)
			{
				il c = graph[b][i];
				if(dist[c.first]==-1||dist[c.first] > dist[b] + c.second)
				{
					dist[c.first] = dist[b] + c.second;
					pq.push(li(dist[c.first],c.first));
				}
			}
		}
	}
}
int main()
{
	int n,m,i,x,y;
	ll w;
	cin>>n>>m;
	graph.assign(n+1,vil());
	dist.assign(n+1,-1);
	for(i=1;i<=n;++i)
	{
		graph[i].push_back(il(i-1,0ll));
	}
	for(i=1;i<=m;++i)
	{
		cin>>x>>y>>w;
		graph[x].push_back(il(y,w));
		graph[y].push_back(il(x,w));
	}
	dijkstra();
	printf("%lld",dist[n]);
}