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())

# 最小値を求めるセグメント木
def init_min(init_min_val):
    #set_val
    for i in range(n):
        seg_min[i+num_max-1]=init_min_val[i]
    #built
    for i in range(num_max-2,-1,-1) :
        seg_min[i]=min(seg_min[2*i+1],seg_min[2*i+2])

def update_min(k,x):
    k += num_max-1
    seg_min[k] = x
    while k:
        k = (k-1)//2
        seg_min[k] = min(seg_min[k*2+1],seg_min[k*2+2])

def query_min(p,q):
    if q<=p:
        return ide_ele_min
    p += num_max-1
    q += num_max-2
    res=ide_ele_min
    while q-p>1:
        if p&1 == 0:
            res = min(res,seg_min[p])
        if q&1 == 1:
            res = min(res,seg_min[q])
            q -= 1
        p = p//2
        q = (q-1)//2
    if p == q:
        res = min(res,seg_min[p])
    else:
        res = min(min(res,seg_min[p]),seg_min[q])
    return res

#####単位元######
ide_ele_min = 10**20

#num_max:n以上の最小の2のべき乗
# num_max =2**(n-1).bit_length()
num_max = 2**(len(str(bin(n-1))) -2)
seg_min=[ide_ele_min]*2*num_max

update_min(0,0)

rlc = []
for i in range(m):
    l,r,c = map(int,input().split())
    rlc.append((r,l,c))

rlc.sort()

for tmp in rlc:
    r,l,c = tmp
    l = l-1
    r = r-1
    update_min( r, min( query_min(l,r) + c , query_min(r,r+1)) )

ans = query_min(n-1,n)
if(ans == ide_ele_min):
    print(-1)
else:
    print(ans)