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;

const ll INF=1E18+7;
const ll N=1E5+7;
ll n,m;
struct stu{
    ll a,b;
    bool friend operator <(const stu &x,const stu &y){
        return x.b>y.b;
    }
};
vector <stu >ve[N];
bool mark[N];
ll dp[N];
void djstrea(){
    priority_queue<stu>que;
    que.push({1,0});
    dp[1]=0;
    while(que.size()){
        stu x=que.top();
        que.pop();
        if(mark[x.a]) continue ;
        mark[x.a]=1;
        for(ll i=0;i<ve[x.a].size();i++){
            ll dx=ve[x.a][i].a;
            ll dy=ve[x.a][i].b;
            if(dp[dx]>dp[x.a]+dy){
                dp[dx]=dp[x.a]+dy;
                que.push({dx,dp[dx]});
            }
        }
    }
}
int main(){
    cin>>n>>m;
    ll x,y,z;
    for(ll i=1;i<=n;i++) {
        ve[i].push_back({i-1,0});
    }
    for(ll i=0;i<=n;i++) dp[i]=INF;
    for(ll i=1;i<=m;i++){
        cin>>x>>y>>z;
        ve[x].push_back({y,z});
    }
    djstrea();
    if(dp[n]==INF)   cout<<-1<<endl;
    else cout<<dp[n]<<endl;
    return 0;
}