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 sys
from heapq import heapify, heappush, heappop
read = sys.stdin.read


def main():
    N, M, *LRC = map(int, read().split())
    graph = [[(0, i - 1)] for i in range(N + 1)]
    graph[1] = []

    for L, R, C in zip(*[iter(LRC)] * 3):
        graph[L].append((C, R))

    distance = [-1] * (N + 1)
    queue = []
    heapify(queue)
    heappush(queue, (0, 1))

    while queue:
        cost, node = heappop(queue)
        if distance[node] == -1:
            distance[node] = cost
            for add_cost, next_node in graph[node]:
                if distance[next_node] == -1:
                    heappush(queue, (cost + add_cost, next_node))

    print(distance[-1])


if __name__ == '__main__':
    main()