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:
n, m = map(int, input().split())
inf = 10 ** 15
edges = [[] for _ in range(n)]
for _ in range(m):
    l, r, c = map(int, input().split())
    edges[l-1].append((r-1, c))
for i in range(n-1):
    edges[i+1].append((i, 0))

from heapq import heappop, heappush
d = [inf for _ in range(n)]
def dijkstra(s):
    que = []
    d[s] = 0
    heappush(que, (0, s))

    while len(que):
        dist, node = heappop(que)

        if d[node] < dist:
            continue
        for to, cost in edges[node]:
            if d[to] > dist + cost:
                d[to] = dist + cost
                heappush(que, (d[to], to))

dijkstra(0)

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