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 sys
input=sys.stdin.readline
import heapq
n,m=map(int,input().split())

D=[0]
P=[]
ans=float("inf")

for i in range(m):
  l,r,c=map(int,input().split())
  P.append((l,r,c))
P.sort(key=lambda x:x[0])
heapq.heappush(D,0*10**15+1)
for l,r,c in P:
  while D:
    ld=heapq.heappop(D)
    dd=ld//(10**15)
    ll=ld%(10**15)
    if ll<l:
      continue
    else:
      break
  if ll>=l:
    heapq.heappush(D,r+(dd+c)*10**15)
  heapq.heappush(D,ll+dd*10**15)
while D:
  ld=heapq.heappop(D)
  dd=ld//(10**15)
  ll=ld%(10**15)
  if ll==n:
    ans=min(ans,dd)
print(-1 if ans==float("inf") else ans)