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:
def update(k,x):
  k+=N0-1
  data[k]=x
  while k>=0:
    k=~-k//2
    data[k]=min(data[2*k+1],data[2*k+2])
def query(l,r):
  L,R=l+N0,r+N0
  s=INF
  while L<R:
    if R&1:
      R-=1
      s=min(s,data[R-1])
    if L&1:
      s=min(s,data[L-1])
      L+=1
    L//=2
    R//=2
  return s
n,m,*t=map(int,open(0).read().split())
N0=2**(n).bit_length()
INF=10**18
data=[INF]*2*N0
update(1,0)
for l,r,c in sorted(zip(*[iter(t)]*3)):update(r,min(data[r+N0-1],query(l,r)+c))
print(data[n+N0-1]%INF or-1)