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:
def main():
    import sys
    input = sys.stdin.readline

    INF = 10 ** 18

    N, M = map(int, input().split())

    G = [[] for _ in range(N + 1)]
    for _ in range(M):
        L, R, C = map(int, input().split())
        G[L].append([C, R])
        G[R].append([C, L])

    for i in range(1, N):
        G[i + 1].append([0, i])

    d = [INF] * (N + 1)

    def dijkstra(s):
        from heapq import heappop, heappush
        d[s] = 0
        pque = []
        heappush(pque, [0, s])
        
        while pque:
            p = heappop(pque)
            v = p[1]
            if d[v] < p[0]:
                continue
            for i in range(len(G[v])):
                e = G[v][i]
                if d[e[1]] > d[v] + e[0]:
                    d[e[1]] = d[v] + e[0]
                    heappush(pque, [d[e[1]], e[1]])

    dijkstra(1)

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

if __name__ == '__main__':
    main()