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 bisect import bisect_left

N, M = map(int, input().split())
LRC = []

for _ in range(M) :
    L, R, C = map(int, input().split())
    LRC.append((L-1, R-1, C))
    
LRC.sort()
LRC.sort(key=lambda x: x[1])

cost_r = [0]
cost_v = [0]
for L, R, C in LRC :
    i = bisect_left(cost_r, L)
    if i == len(cost_r) :
        continue
    nc = cost_v[i] + C
    
    while nc < cost_v[-1] :
        cost_r.pop()
        cost_v.pop()
    
    if R > cost_r[-1] :
        cost_r.append(R)
        cost_v.append(nc)
    
if cost_r[-1] == N - 1 :
    print(cost_v[-1])
else :
    print(-1)