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

def main():
    n, m = map(int, input().split())
    dics = [{} for _ in range(n)]
    for _ in range(m):
        l, r, c = map(int, input().split())
        ky = r-1
        if ky in dics[l-1]:
            if c < dics[l-1][ky]:
                dics[l-1][ky] = c
        else:
            dics[l-1][ky] = c
    dist = [float("inf")]*n
    dist[0] = 0
    hq = []
    heapq.heappush(hq, [0, 0])
    idx = 0
    while len(hq) > 0:
        v, p = heapq.heappop(hq)
        if p < idx:
            continue
        if p == n-1:
            break
        for i in range(idx+1, p):
            if len(dics[i]) > 0:
                for ky in dics[i].keys():
                    if ky in dics[p]:
                        if dics[p][ky] > dics[i][ky]:
                            dics[p][ky] = dics[i][ky]
                    else:
                        if p < ky:
                            dics[p][ky] = dics[i][ky]
        idx = p
        for r in dics[p].keys():
            if dist[r] > v + dics[p][r]:
                dist[r] = v + dics[p][r]
                heapq.heappush(hq, [v + dics[p][r], r])
    if dist[n-1] == float("inf"):
        print(-1)
    else:
        print(dist[n-1])

if __name__ == "__main__":
    main()