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 heapq
N, M = map(int, input().split())
edge_list = [[] for i in range(N+1)]
for i in range(2, N + 1):
    edge_list[i].append((0, i-1))
for i in range(M):
    L, R, C = map(int, input().split())
    edge_list[L].append((C, R))
def solve(s, t):
    fixed = {}
    q = []
    heapq.heappush(q, (0, s))
    while q:
        w, x = heapq.heappop(q)
        if x == t:
            return w
        if x in fixed:
            continue
        fixed[x] = w
        for c, y in edge_list[x]:
            if y not in fixed:
                heapq.heappush(q, (w + c, y))
    return None

answer = solve(1, N)
if answer is None:
    print(-1)
else:
    print(answer)