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())
lst = []
for i in range(m):
    lsti = list(map(int, input().split()))
    lst.append(lsti)

lst.sort(key= lambda x: x[2], reverse=True)
lst.sort(key= lambda x: x[0])

d = [10**18 for i in range(n+1)]
d[1] = 0
for lsti in lst:
    l = lsti[0]
    r = lsti[1]
    c = lsti[2]
    if l == 1:
        for i in range(l+1, r+1):
            d[i] = c
    else:
        for i in range(l+1, r+1):
            j = l+1+r-i
            if d[l]+c < d[j]:
                d[j] = d[l] + c
            else:
                break

if d[n] == 10**18:
    print(-1)
else:
    print(d[n])