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:
//              +-- -- --++-- +-In the name of ALLAH-+ --++-- -- --+              \\

#include <bits/stdc++.h>

#define int ll

#define F first
#define S second
#define _sz(x) (int)x.size()
#define pb push_back

#define error(x) cout << #x << " = " << x << endl

using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;

const int N = 1e5 + 20, inf = 3e18 + 20;
int n, m;
vector <pii> g[N];

int dist[N];

int32_t main()
{
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);

	cin >> n >> m;

	for (int i = 0; i < n - 1; i++)
		g[i + 1].pb({i, 0});

	for (int i = 0, l, r, c; i < m; i++)
	{
		cin >> l >> r >> c;
		l--, r--;
	
		g[l].pb({r, c});
	}
	
	set <pii> st;
	for (int i = 0; i < n; i++) dist[i] = inf;
	
	dist[0] = 0;
	st.insert({0, 0});

	while (_sz(st))
	{
		int v = st.begin() -> S;
		st.erase(st.begin());

		for (pii p : g[v])
		{
			int u = p.F, w = p.S;

			if (dist[v] + w < dist[u])
			{
				st.erase({dist[u], u});
				dist[u] = dist[v] + w;
				st.insert({dist[u], u});
			}
		}
	}

	if (dist[n - 1] == inf) dist[n - 1] = -1;

	cout << dist[n - 1] << '\n';
}