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 sys
input = sys.stdin.readline
sys.setrecursionlimit(pow(10, 6))

from heapq import heappop, heappush


def main():
    n, m = map(int, input().split())
    edges = [[] for _ in range(n)]
    for i in range(1, n):
        edges[i] = [(i - 1, 0)]
    
    lrc = [tuple(map(int, input().split())) for _ in range(m)]
    for l, r, c in lrc:
        edges[l - 1].append((r - 1, c))

    d = [float("inf") for _ in range(n)]
    d[0] = 0
    h = [(0, 0)]
    while len(h) > 0:
        tmpd, tmpi = heappop(h)
        for toi, tod in edges[tmpi]:
            if d[toi] > tmpd + tod:
                d[toi] = tmpd + tod
                heappush(h, (d[toi], toi))
    
    if d[n - 1] == float("inf"):
        print(-1)
    else:
        print(d[n - 1])
    


if __name__ == '__main__':
    main()