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:
class SegmentTree():
  def __init__(self, n, INF):
    self.n = n
    self.INF = INF
    self.log = (n - 1).bit_length()
    self.size = 1 << self.log
    self.data = [self.INF] * (2 * self.size)
  
  def get(self, p):
    #assert 0 <= p < self.n
    res = self.INF
    p += self.size
    for _ in range(self.log+1):
      res = min(res, self.data[p])
      p >>= 1
    return res

  def set(self, p, x):
    #assert 0 <= p < self.n
    p += self.size
    self.data[p] = x

  def range_set(self, l, r, x):
    #assert 0 <= l <= r <= self.n
    l += self.size
    r += self.size
    while l < r:
      if l & 1:
        self.data[l] = min(self.data[l], x)
        l += 1
      if r & 1:
        r -= 1
        self.data[r] = min(self.data[r], x)
      l >>= 1
      r >>= 1

import sys
input = sys.stdin.readline

N, M = map(int, input().split())
INF = 10**18
lst = SegmentTree(N,INF)
lst.set(0,0)
A = [list(map(int, input().split())) for _ in range(M)]
A.sort(key=lambda x:(x[0],x[1]))
for l,r,c in A:
  lst.range_set(l-1,r,lst.get(l-1)+c)
ans = lst.get(N-1)
print(ans if ans<INF else -1)