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 heappop, heappush, heapify

def dijkstra(s, t, links):
    """Dijkstra algorism
    s: int, start node.
    t: int, target node.
    links: iterable, link infomation.
           links[i] contains edges from node i: (cost, target_node).

    return int, minimal cost from s node to t node.
    """
    heap = list(links[s])
    heapify(heap)
    visited = set()
    while len(heap) > 0:
        cost, node = heappop(heap)
        if node == t:
            return cost

        if node in visited:
            continue

        visited.add(node)
        for cost2, node2 in links[node]:
            if node2 in visited:
                continue

            heappush(heap, (cost + cost2, node2))

    return -1

def main():
    input = sys.stdin.readline
    N, M = map(int, input().split())
    links = [[] for _ in range(N)]
    for i in range(1, N):
        links[i].append((0, i-1))

    for _ in range(M):
        l, r, c = map(int, input().split())
        links[l-1].append((c, r-1))
    
    return dijkstra(0, N-1, links)
    

if __name__ == '__main__':
    print(main())