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;
typedef double D;
typedef pair<ll,ll> P;
#define M 998244353
#define F first
#define S second
#define PB push_back
#define INF 100000000000000000
struct SEG{
	ll seg[1<<18];
	SEG(void){
		for(int i=0;i<1<<18;i++)seg[i]=INF;
	}
	void up(int a,ll x){
		a+=(1<<17)-1;
		seg[a]=min(seg[a],x);
		while(a>0){
			a=(a-1)/2;
			seg[a]=min(seg[a*2+1],seg[a*2+2]);	
		}
	}
	ll que(int a,int b,int l,int r,int k){
		if(b<l||r<a)return INF;
		if(a<=l&&r<=b)return seg[k];
		return min(que(a,b,l,(l+r-1)/2,k*2+1),que(a,b,(l+r+1)/2,r,k*2+2));
	}
};
ll n,dp[100005],m;
vector<P>r[100005];
SEG seg;
int main(void){
	cin>>n>>m;
	for(int i=0;i<n;i++)dp[i]=INF;
	for(int i=0;i<m;i++){
		ll l,y,c;
		cin>>l>>y>>c;
		r[--y].PB(P(--l,c));
	}
	dp[0]=0;
	for(int i=0;i<n;i++){
		for(int j=0;j<r[i].size();j++){
			ll l=r[i][j].F,c=r[i][j].S;
			dp[i]=min(dp[i],seg.que(l,i-1,0,(1<<17)-1,0)+c);
		}
		seg.up(i,dp[i]);
	}
	if(dp[n-1]==INF)dp[n-1]=-1;
	cout<<dp[n-1]<<endl;
}