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:
# shortest path on line

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

graph = {i: {} for i in range(1, n + 1)}

for i in range(1, n):
    graph[i + 1][i] = 0

for _ in range(m):
    l, r, c = map(int, input().split())
    if not (r in graph[l].keys()):
        graph[l][r] = c
    else:
        graph[l][r]=min(graph[l][r],c)


###############################################################

import heapq

def dijkstra(s, graph, n):
    # ｓからのグラフの最短最短距離をまとめたデータを返す
    dist = [10**20 for i in range(n + 1)]
    dist[s] = 0
    pq = []
    heapq.heapify(pq)
    # 全ての接点を一度優先度付きキューに挿入する
    heapq.heappush(pq, (0, s))
    while pq:
        x = heapq.heappop(pq)
        node, mini_dis = x[1], x[0]
        for point in graph[node].keys():
            w = graph[node][point]
            # nodeからpointに対して伸びる辺の長さ
            newlen = dist[node] + w
            if newlen < dist[point]:
                heapq.heappush(pq, (newlen, point))
                dist[point] = newlen

    return dist
###############################################################


A = dijkstra(1, graph, n)
if A[n]<10**20:
    print(A[n])
else:
    print(-1)