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
sys.setrecursionlimit(2147483647)
INF=float("inf")
MOD=10**9+7
input=lambda :sys.stdin.readline().rstrip()
class SegmentTree(object):
    def __init__(self,A,dot,e):
        n=2**((len(A)-1).bit_length())
        self.__n=n
        self.__dot=dot
        self.__e=e
        self.__node=[e]*(2*n)
        for i in range(len(A)):
            self.__node[i+n]=A[i]
        for i in range(n-1,-0,-1):
            self.__node[i]=dot(self.__node[2*i],self.__node[2*i+1])

    def add(self,i,c):
        i+=self.__n
        node=self.__node
        node[i]=self.__dot(c,node[i])
        while(i!=1):
            i//=2
            node[i]=self.__dot(node[2*i],node[2*i+1])

    def sum(self,l,r):
        vl,vr=self.__e,self.__e
        l+=self.__n; r+=self.__n
        while(l<r):
            if(l%2==1):
                vl=self.__dot(vl,self.__node[l])
                l+=1
            l//=2
            if(r%2==1):
                r-=1
                vr=self.__dot(self.__node[r],vr)
            r//=2
        return self.__dot(vl,vr)

def resolve():
    n,m=map(int,input().split())
    LRC=[0]*m
    for i in range(m):
        l,r,c=map(int,input().split())
        l-=1
        LRC[i]=(l,r,c)
    LRC.sort()

    A=[INF]*n
    A[0]=0
    tree=SegmentTree(A,min,INF)
    for l,r,c in LRC:
        s=tree.sum(l,r)
        tree.add(r-1,s+c)

    ans=tree.sum(n-1,n)
    if(ans==INF): ans=-1
    print(ans)
resolve()