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 sys import stdin
import heapq

N, M = [int(x) for x in stdin.readline().rstrip().split()]
B = [[int(x) for x in stdin.readline().rstrip().split()] for _ in range(M)]

graph = [[] for _ in range(N)]
for i in range(1, N):
    graph[i].append((0, i - 1))
for m in B:
    graph[m[0] - 1].append((m[2], m[1] - 1))

d = [(0, 0)]
distance = [10 ** 15] * N
distance[0] = 0
color = ['white'] * N
heapq.heapify(d)

while len(d) > 0:
    temp, u = heapq.heappop(d)
    color[u] = 'black'
    if distance[u] < temp:
        continue
    for v in graph[u]:
        if color[v[1]] != 'black':
            if distance[u] + v[0] < distance[v[1]]:
                distance[v[1]] = distance[u] + v[0]
                color[v[1]] = 'gray'
                heapq.heappush(d, (distance[v[1]], v[1]))

if distance[N - 1] == 10 ** 15:
    print(-1)
else:
    print(distance[N - 1])