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<cstdio>
#include<vector>
#include<algorithm>
using namespace std;
typedef long long ll;
struct node
{
	ll r,c;
}u;
ll j,m,x,n,i,tr[100005],v,l,r,c;
vector<node>s[100005];
const ll inf=1e18;
ll lowbit(ll p){return p&-p;}
ll ask(ll p)
{
	ll ans=inf;
	while(p)
	{
		ans=min(ans,tr[p]);
		p-=lowbit(p);
	}
	return ans;
}
void modify(ll p)
{
	while(p<=n)
	{
		tr[p]=min(tr[p],v);
		p+=lowbit(p);
	}
}
int main()
{
	scanf("%lld%lld",&n,&m);
	for(i=1;i<=n;i++)tr[i]=inf;
	for(i=1;i<=m;i++)
	{
		scanf("%lld%lld%lld",&l,&r,&c);
		s[l].push_back((node){r,c});
	}
	v=0;
	modify(n);
	for(i=n-1;i>0;i--)
	{
		v=inf;
		for(j=0;j<s[i].size();j++)
		{
			u=s[i][j];
			v=min(v,ask(u.r)+u.c);
		}
		modify(i);
	}
	if(v>=inf)printf("-1\n");
	else printf("%lld\n",v);
	return 0;
}