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

INF = 2**62-1

def dijkstra(route_map, start_point):
    num_of_city = len(route_map)
    dist = [INF for _ in range(num_of_city)]

    dist[start_point] = 0
    heap_q = []
    heapq.heappush(heap_q, (0, start_point))
    while heap_q:
        prev_cost, src = heapq.heappop(heap_q)

        if dist[src] < prev_cost:
            continue

        for dest, cost in route_map[src].items():
            if dist[dest] > dist[src] + cost:
                dist[dest] = dist[src] + cost
                heapq.heappush(heap_q, (dist[dest], dest))
    return dist

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

for i in range(m):
    u, v, a = list(map(int, input().split()))
    u, v = u - 1, v - 1
    if v in route_map[u].keys():
        a = min(a, route_map[u][v])
    route_map[u][v] = a

for i in range(n-1):
    u, v = i+1, i
    route_map[u][v] = 0

# ゴールまでの最短経路
dijkstra_result = dijkstra(route_map, 0)

if dijkstra_result[-1] != INF:
    print(dijkstra_result[-1])
else:
    print(-1)