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:
def main():    
    n,m = map(int,input().split())
    lrc = [tuple(map(int,input().split())) for _ in range(m)]
    lcr = sorted([(i[0]-1,i[2],i[1]-1) for i in lrc],reverse=True)
    INF = float('inf')
    dist = [INF]*n
    check = [False]*n
    check[0] = True
    dist[0] = 0
    enable = True
    while lcr:
        route = lcr.pop(-1)
        mn = route[0]
        mx = route[-1]
        if not check[mn]:
            enable = False
            break
        else:
            d = route[1]+dist[mn]
            for i in range(mx,mn,-1):
                if dist[i] >= d:
                    dist[i] = d
                    check[i] = True
                else:
                    break
    if dist[-1] == INF:
        print(-1)
    elif enable:
        print(dist[-1])
    else:
        print(-1)
    
if __name__ == '__main__':
    main()