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 N=1e5+5,inf=1e18;
ll l[N],r[N],c[N],dp[N];
vector<ll> ent[N],ext[N];
int main(){
    ios_base:: sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    ll n,m;cin>>n>>m;
    for(ll i=1;i<=m;i++){
        cin>>l[i]>>r[i]>>c[i];
        ent[r[i]].push_back(i);
        ext[l[i]].push_back(i);
    }
    for(ll i=1;i<n;i++)dp[i]=inf;
    multiset< pair<ll,ll> > st;
    for(ll i=n;i>=1;i--){
        if(!st.empty())dp[i]=min(dp[i] , st.begin()->first);
        for(auto &id:ent[i])st.insert({dp[r[id]]+c[id],id});
        for(auto &id:ext[i])st.erase({dp[r[id]]+c[id],id});
    }
    if(dp[1]>=inf)cout<<"-1";
    else cout<<dp[1];
}