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())
d = []
for _ in range(m):
  l,r,c = map(int,input().split())
  d.append([l,r,c])
d.sort(key=lambda x:x[0])
g = [float("inf") for _ in range(n+1)]
g[1] = 0
f = 1
for i in range(m):
  if d[i][0] > f:
    print(-1)
    exit()
  f = max(f,d[i][1])
  sm = d[i][2]+g[d[i][0]]
  if g[d[i][1]] > sm:
    g[d[i][1]] = sm
    j = d[i][1]-1
    while g[j] > sm:
      g[j] = sm
      j -= 1
if g[n] != float("inf"):
  print(g[n])
else:
  print(-1)