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:
from heapq import heappop, heappush

n, m = map(int, input().split())
graph = [list() for _ in range(n)]

for i in range(1, n):
    graph[i].append((i-1, 0))

for _ in range(m):
    f, t, c = map(int, input().split())
    f -= 1; t -= 1
    graph[f].append((t, c))

INF = float("inf")
s = 0
d = [0] + [INF] * (n-1)
q = []
heappush(q, (0, s))

while q:
    dist, v = heappop(q)
    if d[v] < dist: continue
    for nv, cost in graph[v]:
        if d[nv] > d[v] + cost:
            d[nv] = d[v] + cost
            heappush(q, (d[nv], nv))

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