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 sys
from heapq import heappop, heappush


def dijkstra(s, t, links):
    q = [(0, s)]
    visited = set()
    while q:
        cost, v = heappop(q)
        if v in visited:
            continue
        if v == t:
            return cost
        visited.add(v)
        for u, c in links[v]:
            if u in visited:
                continue
            heappush(q, (cost + c, u))
    return -1


n, m = list(map(int, input().split()))
links = [set() for _ in range(n)]
for v in range(n - 1):
    links[v + 1].add((v, 0))
for line in sys.stdin:
    l, r, c = map(int, line.split())
    links[l - 1].add((r - 1, c))
print(dijkstra(0, n - 1, links))