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 heapq
def dijkstra_heap(s,g):
    used = [True] * n #True:未確定
    used[s] = False
    edgelist = []
    for e in edge[s]:
        heapq.heappush(edgelist,[e[0],e[1]])
    while len(edgelist):
        minedge = heapq.heappop(edgelist)
        #まだ使われてない頂点の中から最小の距離のものを探す
        if not used[minedge[1]]:
            continue
        v = minedge[1]
        if v==g:
            return minedge[0]
        kai=minedge[0]
        used[v] = False
        for e in edge[v]:
            if used[e[1]]:
                heapq.heappush(edgelist,[kai+e[0],e[1]])                   
    return -1

################################
n,m = map(int,input().split()) #n:頂点数　w:辺の数

edge = [[] for i in range(n)]
#edge[i] : iから出る道の[重み,行先]の配列
l=[]
for i in range(m):
    x,y,z = map(int,input().split())
    edge[x-1].append([z,y-1])
    edge[y-1].append([z,x-1])
    l.append([x-1,y-1])
zeroedge=[0]*n
l.sort()
l.append([10**10,10**10+1])
i=0
nl=l[i][0]
r=l[i][1]
while i<m+1:
    if l[i][0]>r:
        for j in range(nl,r):
            edge[j+1].append([0,j])
        nl=l[i][0]
        r=l[i][1]
        i+=1
    else:
        r=max(r,l[i][1])
        i+=1       
print(dijkstra_heap(0,n-1))