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 heapq

n, m = [int(v) for v in input().split(' ')]

links = []
for i in range(n):
    links.append([])

for i in range(m):
    l, r, c = [int(v) for v in input().split(' ')]
    l -= 1
    r -= 1
    links[r].append((l, c))

h = []
heapq.heappush(h, (0, n-1))
closed = 0
while len(h) > 0:
    c0, n0 = heapq.heappop(h)
    if (closed & (1 << n0)) != 0:
        continue
    closed |= (1 << n0)
    if n0 == 0:
        print(c0)
        exit()

    for n1, c1 in links[n0]:
        if (closed & (1 << n1)) != 0:
            continue
        heapq.heappush(h, (c0 + c1, n1))

    n2 = n0 + 1
    if n2 < n:
        if (closed & (1 << n2)) == 0:
            heapq.heappush(h, (c0, n2))

print("-1")