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:
n,m=map(int,input().split())
lrc=[list(map(int,input().split())) for _ in range(m)]
lrc.sort(key=lambda x:x[0])
# 
inf=float('inf')
seen=[inf]*n
seen[0]=0
now=0
from heapq import heappop,heappush
from collections import deque
lrc=deque(lrc)
todo=[[0,now]]
while todo:
  d,v=heappop(todo)
  lst=[]
  while lrc and lrc[0][0]<=v+1:
    lst.append(lrc.popleft())
  for l,r,c in lst:
    if seen[r-1]>seen[v]+c:
      heappush(todo,[seen[v]+c,r-1])
      seen[r-1]=seen[v]+c
if seen[-1]!=inf:
  print(seen[-1])
else:
  print(-1)
#print(seen)