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:
from heapq import heappush,heappop
n,m=map(int,input().split())
lrc=[list(map(int,input().split())) for i in range(m)]
data=[[] for i in range(n+1)]
for i in range(2,n+1):
    data[i].append([i-1,0])
for u in lrc:
    l,r,c=u
    data[l].append([r,c])
lst=[]
flag=[-1]*(n+1)
flag[1]=0
for u in data[1]:
    heappush(lst,[u[1],u[0]])
while lst:
    c,r=heappop(lst)
    if r==n:
        print(c)
        break
    if flag[r]==-1:
        flag[r]=c
        for u in data[r]:
            if flag[u[0]]==-1:
                heappush(lst,[c+u[1],u[0]])
else:
    print(-1)