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:
# -*- coding: utf-8 -*-
import sys
from bisect import bisect_left,bisect_right
sys.setrecursionlimit(10**9)
INF=10**18
MOD=10**9+7
input=lambda: sys.stdin.readline().rstrip()
YesNo=lambda b: bool([print('Yes')] if b else print('No'))
YESNO=lambda b: bool([print('YES')] if b else print('NO'))
int1=lambda x:int(x)-1

N,M=map(int,input().split())

edge=[[] for _ in range(N)]
for i in range(N-1):
    edge[i+1].append((0,i))
for _ in range(M):
    l,r,c=map(int,input().split())
    l-=1
    r-=1
    edge[l].append((c,r))

from heapq import heappop,heappush
# edges=[[(cost1,v1),(cost2,v2)],...]
def dijkstra(start,n,edges):
    d=[INF]*n
    used=[False]*n
    d[start]=0
    used[start]=True
    edgelist=[]
    for edge in edges[start]:
        heappush(edgelist,edge)
    while edgelist:
        minedge=heappop(edgelist)
        if used[minedge[1]]:
            continue
        v=minedge[1]
        d[v]=minedge[0]
        used[v]=True
        for edge in edges[v]:
            if not used[edge[1]]:
                heappush(edgelist,(edge[0]+d[v],edge[1]))
    return d

d=dijkstra(0,N,edge)
print(d[-1] if d[-1]!=INF else -1)