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 heapq
import sys
input = sys.stdin.readline

n, m = map(int, input().split())

edges = [[] for _ in range(n)]
for i in range(1, n):
    _from, to, dist = i, i-1, 0
    edges[_from].append([to, dist])

for _ in range(m):
    _from, to, dist = map(int, input().split())
    edges[_from-1].append([to-1, dist])


D = [float('INF')]*n
D[0] = 0
todo = []
for to, dist in edges[0]:
    heapq.heappush(todo, [dist, to])
    D[to] = dist

while todo:
    total_dist, node = heapq.heappop(todo)

    for to, dist in edges[node]:
        if total_dist + dist < D[to]:
            heapq.heappush(todo, [total_dist+dist, to])
            D[to] = total_dist + dist
        else:
            continue

ans = D[n-1]
if ans == float('INF'):
    ans = -1

print(ans)