p02868 NIKKEI Programming Contest 2019-2 - Shortest Path on a Line
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
```python
from heapq import heappush,heappop
N,M=map(int,input().split())
LRC=[list(map(int,input().split())) for i in range(M)]
data=[[],[]]+[[[i-1,0]] for i in range(2,N+1)]
for L,R,C in LRC:
    data[L].append([R,C])
dist=[[0,1]]
inf=float("inf")
flag=[inf]*(N+1)
while dist:
    y,x=heappop(dist)
    if flag[x]!=inf:
        continue
    flag[x]=y
    for u in data[x]:
        if flag[u[0]]==inf:
            heappush(dist,[y+u[1],u[0]])
    if flag[N]!=inf:
        break
if flag[N]==inf:
    print(-1)
else:
    print(flag[N])
```