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())

import heapq
def dijkstra_heap(s):
  #始点sから各頂点への最短距離と直前の点
  dist=[float("inf")]*size_v
  prev=[-1]*size_v
  used=[False]*size_v
  #used=set()
  dist[s]=0
  used[s]=True
  #used.add(s)

  hq_edge=[]
  for v,w in graph[s]:
    heapq.heappush(hq_edge,(w,v,s))

  while hq_edge:
    min_w,min_v,u=heapq.heappop(hq_edge)
    #まだ使われてない頂点の中から最小の距離のものを探す
    if used[min_v]:
    #if min_v in used:
      continue

    dist[min_v]=min_w
    prev[min_v]=u
    used[min_v]=True
    #used.add(min_v)
    for v,w in graph[min_v]:
      if not used[v]: 
      #if not v in used:
        heapq.heappush(hq_edge,(min_w+w,v,min_v))

  return dist,prev

size_v=N+1
s=1

graph=[[] for _ in range(size_v)]
for i in range(2,N):
  graph[i].append((i-1,0))
for _ in range(M):
  L,R,C=map(int,input().split())
  graph[L].append((R,C))
  
dist,prev=dijkstra_heap(s)
#print(dist)
if dist[N]==float("inf"):
  print(-1)
else:
  print(dist[N])