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
import collections
def main():

    N, M = map(int, input().split())
    graph = collections.defaultdict(dict)
    for i in range(N-1):
        graph[i+1][i] = 0

    for _ in range(M):
        L, R, C = map(int, input().split())
        if L-1 in graph and R-1 in graph[L-1]:
            graph[L-1][R-1] = min(graph[L-1][R-1], C)
        else:
            graph[L-1][R-1] = C

    dist = [float('inf') for _ in range(N)]
    dist[0] = 0
    v = []
    heapq.heappush(v, [0, 0])

    while len(v) > 0:
        d, u = heapq.heappop(v)
        if d > dist[u]: continue
        for w in graph[u]:
            if dist[w] > d + graph[u][w]:
                dist[w] = d + graph[u][w]
                heapq.heappush(v, [dist[w], w])

    if dist[N-1] == float('inf'): return -1

    return dist[N-1]

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