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
read=sys.stdin.readline

class segtree:
    def __init__(self,n,op,e):
        self.e=e
        self.op=op
        self.size=1<<(n-1).bit_length()
        self.SEG=[self.e]*(self.size*2)
    
    def update(self,i,x):
        i+=self.size
        self.SEG[i]=x
        
        while i>0:
            i>>=1
            self.SEG[i]=self.op(self.SEG[i*2],self.SEG[i*2+1])
    
    def get(self,i):
        return self.SEG[i+self.size]
    
    def query(self,l,r):
        l+=self.size
        r+=self.size
        
        lres,rres=self.e,self.e
        
        while l<r:
            if l&1:
                lres=self.op(lres,self.SEG[l])
                l+=1
            
            if r&1:
                r-=1
                rres=self.op(rres,self.SEG[r])
            
            l>>=1
            r>>=1
            
        res=self.op(lres,rres)
        return res

INF=float('inf')
N,M=map(int,read().split())

Q=[]
for i in range(M):
    l,r,c=map(int,read().split())
    Q.append((l-1,r-1,c))
Q.sort(key=lambda x:x[0])

seg=segtree(N,min,INF)
seg.update(0,0)
for L,R,C in Q:
    res=seg.query(L,R)+C
    if seg.get(R)>res:
        seg.update(R,res)
ans=seg.get(N-1)
print(ans if ans!=INF else -1)