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 <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#define PII pair<int,int>
#define MP make_pair
#define fir first
#define sec second
#define PB push_back
#define ll long long
using namespace std;
template <class T>
inline void rd(T &x) {
	x=0; char c=getchar(); int f=1;
	while(!isdigit(c)) { if(c=='-') f=-1; c=getchar(); }
	while(isdigit(c)) x=x*10-'0'+c,c=getchar(); x*=f;
}
const int N=1e5+10;
const ll inf=1e18;
int n,m;
ll c[N];
void add(int i,ll t) { for(;i;i-=i&-i) c[i]=min(c[i],t); }
ll query(int i) { ll ans=inf; for(;i<=n;i+=i&-i) ans=min(ans,c[i]); return ans; }
vector<PII > G[N];
ll f[N];
int main() {
	rd(n),rd(m);
	for(int l,r,c,i=1;i<=m;++i) {
		rd(l),rd(r),rd(c);
		G[r].PB(MP(l,c));
	}
	memset(f,0x3f,sizeof(f));
	memset(c,0x3f,sizeof(c));
	f[1]=0,add(1,0);
	for(int i=2;i<=n;++i) {
		for(int j=0;j<G[i].size();++j)
			f[i]=min(f[i],query(G[i][j].fir)+G[i][j].sec);
		add(i,f[i]);
	}
	if(f[n]>1e16) printf("-1");
	else printf("%lld\n",f[n]);
	return 0;
}