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
import heapq
n, m = map(int, input().split())

nextL = [[] for _ in range(n+1)]
for i in range(2, n+1):
    nextL[i].append([i-1, 0])

INF = 10**18

costs = [INF] * (n+1)
costs[1] = 0

for i in range(m):
    l, r, c = map(int, sys.stdin.readline().split())
    nextL[l].append([r, c])

pc = []
heapq.heappush(pc, (0, 1))

unreach = set(range(1, n+1))

while len(pc) > 0 :
    cost, target = heapq.heappop(pc)
    if cost > costs[target]:
        continue
    for i in nextL[target]:
        nex = i[0]
        cos = i[1]
        if nex in unreach and cost + cos < costs[nex]:
            costs[nex] = cost + cos
            heapq.heappush(pc, (cost+cos, nex))
    unreach.remove(target)

if costs[n] == INF:
    print(-1)
else:
    print(costs[n])