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 numpy as np
#from numpy import*
#from scipy.sparse.csgraph import shortest_path #shortest_path(csgraph=graph) # dijkstra# floyd_warshall
#from scipy.sparse import csr_matrix
from collections import* #defaultdict Counter deque appendleft
from fractions import gcd
from functools import* #reduce
from itertools import* #permutations("AB",repeat=2) combinations("AB",2) product("AB",2) groupby accumulate
from operator import mul,itemgetter
from bisect import* #bisect_left bisect_right
from heapq import* #heapify heappop heappushpop
from math import factorial,pi
from copy import deepcopy
import sys
sys.setrecursionlimit(10**8)
#input=sys.stdin.readline
input=sys.stdin.readline

n,m=map(int,input().split())

def DIJKSTRA(point,d):
    cost      = [float("inf")]*(n+1)
    Q         = []
    cost[point]=0
    heappush(Q,(point,cost[point]))
    while Q:
        prefnd,tmpC=heappop(Q)
        if cost[prefnd]<tmpC:
            continue
        for node,c in d[prefnd]:
            altC=c+tmpC
            if cost[node]>altC:
                cost[node]=altC
                heappush(Q,(node,altC))
    return cost

def main():
    
    d=[[]for i in range(n+1)]
    
    for i in range(m):
        a,b,c=map(int,input().split())
        d[a].append((b,c))
    for i in range(1,n+1):
        d[i].append((i-1,0))
#    print(d)
    x=DIJKSTRA(1,d)[n]
    if x!=float("inf"):
        print(x)
    else:
        print(-1)
        
if __name__ == '__main__':
    main()