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
input = sys.stdin.readline

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


#Starry sky tree(一点取得、範囲min更新の1-indexed Segment tree. Aは0-indexedなことに注意.



seg_el=1<<((N+1).bit_length())# Segment treeの台の要素数
SEG=[1<<60]*(2*seg_el)# 1-indexedなので、要素数2*seg_el.Segment treeの初期値で初期化
SEG[1+seg_el]=0

def getvalue(n,seg_el):# 一点の値を取得
    i=n+seg_el
    ANS=1<<60
    
    ANS=min(SEG[i],ANS)
    i>>=1# 子ノードへ
    
    while i!=0:
        ANS=min(SEG[i],ANS)
        i>>=1

    return ANS

def updates(l,r,x):# 区間[l,r)のminを更新.
    L=l+seg_el
    R=r+seg_el

    while L<R:
        if L & 1:
            SEG[L]=min(x,SEG[L])
            L+=1

        if R & 1:
            R-=1
            SEG[R]=min(x,SEG[R])
        L>>=1
        R>>=1

for l,r,c in B:
    x=getvalue(l,seg_el)
    updates(l,r+1,x+c)

if getvalue(N,seg_el)==1<<60:
    print(-1)
else:
    print(getvalue(N,seg_el))