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())
E = [[int(e) for e in input().split()] for _ in range(M)]

E.sort()
inf = 10**15
seg = [inf]*(2*N-1)

def update(k, x):
    k += N-1
    seg[k] = x
    while k:
        k = (k-1)//2
        seg[k] = min(seg[2*k+1], seg[2*k+2])
        
def query(p, q):
    p += N-1
    q += N-2
    res = inf
    while q-p > 1:
        if p&1 == 0:
            res = min(res, seg[p])
        if q&1 == 1:
            res = min(res, seg[q])
            q -= 1
        p //= 2
        q = (q-1)//2
    if p == q:
        res = min(res, seg[q])
    else:
        res = min(res, seg[p], seg[q])
    return res

update(0, 0)
for e in E:
    d = query(e[1]-1, N)
    l = query(e[0]-1, N)
    if l+e[2] < d:
        update(e[1]-1, l+e[2])

if seg[-1] == inf:
    print(-1)
else:
    print(seg[-1])