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
input=sys.stdin.readline
import heapq

def dijkstra(Route,v,start):
    Dist=[float('inf')]*v
    Dist[start]=0
    Visited=[False]*v
    hq=[(0,start)]
    while hq:
        dist,fr=heapq.heappop(hq)
        Visited[fr]=True
        for to,cost in Route[fr]:
            if (not Visited[to]) and Dist[to]>dist+cost:
                Dist[to]=dist+cost
                heapq.heappush(hq,(Dist[to],to))
    return Dist

def main():
    n,m=map(int,input().split())
    Edges=[[] for _ in range(n)]
    for i in range(n-1):
        Edges[i+1].append((i,0))
    for _ in range(m):
        l,r,c=map(int,input().split())
        l-=1; r-=1
        Edges[l].append((r,c))
    Dist=dijkstra(Edges,n,0)
    print(-1 if Dist[-1]==float('inf') else Dist[-1])
    
if __name__=='__main__':
    main()