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 PYTHON3):

Solution:
from heapq import *


def Dijkstra(G: list, source=0):
	INF = float("inf")
	V = len(G)
	D = [INF] * V
	vis = [False] * V
	H = [(0, source)]
	while H:
		dist, cur = heappop(H)
		if vis[cur]:
			continue
		vis[cur] = True
		for nxt, cost in G[cur]:
			t = dist + cost
			if D[nxt] > t:
				D[nxt] = t
				heappush(H, (t, nxt))
	return D[-1] if D[-1]!=INF else -1


N, M, *L = map(int, open(0).read().split())
G = [[(i - 1, 0)] for i in range(N)]
G[0] = []
for l, r, c in zip(*[iter(L)] * 3):
	G[l - 1].append((r - 1, c))
print(Dijkstra(G))