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 getN():
    return int(input())
def getNM():
    return map(int, input().split())
def getList():
    return list(map(int, input().split()))
import heapq
# import math
INF = 10**11

def main():
    n, m= getList()
    begin = [[] for i in range(n)]
    cost = [-1 for i in range(n)]
    for i in range(m):
        st, en, cos = getList()
        begin[st-1].append((cos, en-1))

    h = []
    for warp in begin[0]:
        heapq.heappush(h, warp)
    cur_mas = 0

    while(h):
        cand = heapq.heappop(h)
        if cand[1] > cur_mas:
            # 歩を1つ進め、その場所を更新
            cur_mas += 1
            cost[cur_mas] = cand[0]
            for warp in begin[cur_mas]:
                # そこまでの距離とコストを足す
                tcos, ten = warp[0] + cost[cur_mas], warp[1]
                heapq.heappush(h, (tcos, ten))
            heapq.heappush(h, cand)



    print(cost[n-1])
if __name__ == "__main__":
    main()