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
import heapq
input = sys.stdin.readline
heapify, push, pop = heapq.heapify, heapq.heappush, heapq.heappop

_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()


def chker(n, m, lrc):
    dst = [float('inf')] * n
    dst[0] = 0
    q = [(0, 0)]

    cnt = 0
    for i in range(n):
        while q:
            d, r = q[0]
            if i <= r:
                break
            pop(q)
        else:
            print(-1)
            return

        dst[i] = d
        while cnt < m and lrc[cnt][0] == i:
            l, r, c = lrc[cnt]
            push(q, (d + c, r))
            cnt += 1

    print(dst[-1])


chker(_n, _m, _lrc)