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:
# instead of AVLTree

INF = 10**14

class BIT():
    def __init__(self, max):
        self.max = max
        self.data = [INF]*(self.max+1)
    
    def update(self, i, x):
        while i > 0:
            self.data[i] = min(self.data[i], x)
            i -= i & -i

    def read(self, i):
        m = INF
        while i <= self.max:
            m = min(self.data[i], m)
            i += i & -i
        return m

import sys
input = sys.stdin.readline
from operator import itemgetter

N, M = map(int, input().split())
LRC = [list(map(int, input().split())) for _ in range(M)]
LRC.sort(key=itemgetter(0))

bit = BIT(N)
bit.update(1, 0)

for l, r, c in LRC:
    m = bit.read(l)
    bit.update(r, m+c)

ans = bit.data[N]
if ans == INF:
    print(-1)
else:
    print(ans)