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>
#define maxl 300010
using namespace std;

int n,m;
long long ans;
int a[maxl];
long long f[maxl];
struct lne
{
	int l,r,c;
};
multiset <long long> s; 
vector <lne> in[maxl],out[maxl];

inline void prework()
{
	scanf("%d%d",&n,&m);
	int l,r,c;
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d%d",&l,&r,&c);
		in[l].push_back(lne{l,r,c});
		out[r].push_back(lne{l,r,c});
	}
}

inline void mainwork()
{
	f[1]=0;
	for(auto d: in[1])
		s.insert(d.c);
	for(int i=2;i<=n;i++)
	{
		if(s.begin()==s.end())
		{
			ans=-1;
			return;
		}
		f[i]=(*s.begin());
		for(auto d: in[i])
			s.insert(f[i]+d.c);
		for(auto d: out[i])
			s.erase(s.lower_bound(f[d.l]+d.c));
	}
	ans=f[n];
}

inline void print()
{
	printf("%lld",ans);
}

int main()
{
	int t=1;
	//scanf("%d",&t);
	for(int i=1;i<=t;i++)
	{
		prework();
		mainwork();
		print();
	}
	return 0;
}