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
from heapq import heappop, heappush
from collections import defaultdict
input = sys.stdin.buffer.readline

INF = 10**20
N,M = map(int,input().split())
g = defaultdict(list)
for i in range(2,N+1):
    g[i].append((i-1,0))
for i in range(1,M+1):
    l,r,c = list(map(int,input().split()))
    g[l].append((r,c))

d = [INF] * (N+1)
d[1] = 0
que = []
heappush(que,(1,0))
while que:
    s, dist = heappop(que)
    if d[s] < dist:
        continue
    for t,c in g[s]:
        if d[t] > d[s] + c:
            d[t] = d[s] + c
            heappush(que,(t,d[t]))
if d[N] == INF:
    print(-1)
    exit()
print(d[N])