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 heapify, heappop, heappush
MAX_INT = int(10e15)
MIN_INT = -MAX_INT
mod = 1000000007
sys.setrecursionlimit(1000000)
def IL(): return list(map(int,input().split()))
def SL(): return input().split()
def I(): return int(sys.stdin.readline())
def S(): return input()

N, M = IL()
LRC = [IL() for _ in range(M)]

root = [[(0, i-1)] for i in range(N+1)] #(cost, vertex)
for i in range(M):
  L, R, C = LRC[i]
  root[L].append((C, R))
#print(root)
data = []
heappush(data, (0, 1)) #(total_cost, vertex)
ans = [MAX_INT]*(N+1)
ans[1] = 0
finished = [False]*(N+1)
finished[0] = True

while data:
  nowcost, v = heappop(data)
  #print(nowcost, v)
  if finished[v] == False:
    finished[v] = True
    for edge, nextv in root[v]:
      if ans[nextv] < nowcost + edge:
        continue
      else:
        ans[nextv] = nowcost + edge
        heappush(data, (nowcost + edge, nextv))
      #print(ans)
if finished[N] == True:
  print(ans[N])
else:
  print(-1)