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
stdin = sys.stdin

sys.setrecursionlimit(10 ** 7)

def li(): return map(int, stdin.readline().split())
def li_(): return map(lambda x: int(x) - 1, stdin.readline().split())
def lf(): return map(float, stdin.readline().split())
def ls(): return stdin.readline().split()
def ns(): return stdin.readline().rstrip()
def lc(): return list(ns())
def ni(): return int(stdin.readline())
def nf(): return float(stdin.readline())

from bisect import bisect_right

n, m = li()
lrc = [list(li()) for _ in range(m)]

# n = 10**5
# m = 10**5
# lrc = [[1, n, 5] for _ in range(m)]

# l -> r の降順にソート
lrc = sorted(lrc, key=lambda x: x[2])
lrc = sorted(lrc, key=lambda x: x[1])
lrc = sorted(lrc, key=lambda x: x[0])
#lrc = sorted((sorted(lrc, key=lambda x: x[1])), key=lambda x: x[0])

# 二分探索で距離更新
INF = float('inf')
dist = [INF]*n
dist[0] = 0

for left_idx, right_idx, ci in lrc:
    left_idx -= 1
    newleft_idx = bisect_right(dist, dist[left_idx] + ci)
    for idx in range(newleft_idx, right_idx):
        dist[idx] = dist[left_idx] + ci

if dist[-1] == INF:
    print(-1)
else:
    print(dist[-1])