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:
from heapq import *
import sys
from collections import *
from itertools import *
from decimal import *
import copy
from bisect import *
import time
import math
sys.setrecursionlimit(4100000)
def gcd(a,b):
    if(a%b==0):return(b)
    return (gcd(b,a%b))

N,M=map(int,input().split())
LRC=[list(map(int,input().split())) for i in range(M)]
LRC.sort()


stack=[[0,-1,0]]
idle_max=10**18
visited=[idle_max for i in range(N+1)]
visited2=[0 for i in range(N+1)]
visited[1]=0
x=0
while stack:
    #print(stack)
    m,a,p=heappop(stack)
    a=-a
    if a==N:
        print(m)
        break
    if not visited2[a]:
        visited2[a]=1
        for i in range(x,M):
            l,r,c=LRC[i]
            x=i
            if l<=a:
                _m=m+c
                if _m<visited[r]:
                    visited[r]=_m
                    heappush(stack,[_m,-r,a+1])
            else:
                break
else:
    print(-1)