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:
#12:00
#解説解答
n,m = map(int,input().split())
inf = 10 ** 18
pst = [[] for _ in range(n)]
for i in range(1,n):
  pst[i].append([0,i-1])
for _ in range(m):
  l,r,c = map(int,input().split())
  l -= 1
  r -= 1
  pst[l].append([c,r])
#print(pst)
import heapq
nxt = pst[0]
heapq.heapify(nxt)
#print(nxt)
seen = [inf for _ in range(n)]
seen[0] = 0
for x in nxt:
  seen[x[1]] = x[0]
while True:
  #print(nxt)
  if nxt == []:
    print(-1)
    break
  c,r = heapq.heappop(nxt)
  if r == n-1:
    print(seen[r])
    break
  for x in pst[r]:
    #print(pst[r])
    #print(x)
    xc,xr = x
    if seen[xr] > seen[r] + xc:
      seen[xr] = seen[r] + xc
      heapq.heappush(nxt,[seen[xr],xr])
#print(seen)