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:
import heapq

N, M = map(int, input().split())

items = []
for _ in range(M):
	l, r, c = map(int, input().split())
	items.append([l, r, c])

items.sort()
def check():
	queue = []
	index = 0
	data = [None]
	dists = [None, 0]
	for i in range(1, N):
		while index < M:
			l, r, c = items[index]
			if l <= i:
				heapq.heappush(queue, (c + dists[i], -r))
				index += 1
			else:
				break
		while True:
			if len(queue) == 0:
				return None
			c, r = queue[0]
			if -r > i:
				break
			heapq.heappop(queue)
		data.append((c, -r))
		dists.append(c)
	return dists

data = check()
if data != None:
	print(data[N])
else:
	print(-1)