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:
from heapq import heapify, heappush, heappop
import sys
input = sys.stdin.readline

INF = float('inf')

def solve():
    N, M = map(int, input().split())
    Es = []
    for _ in range(M):
        L, R, C = map(int, input().split())
        L, R = L-1, R-1
        Es.append((L, R, C))

    Es.sort()

    PQ = [(0, 0)]

    dists = [INF] * N
    iE = 0
    for tm in range(N):
        while PQ:
            dist, R = PQ[0]
            if tm <= R:
                break
            heappop(PQ)
        else:
            return -1

        dists[tm] = dist
        while iE < M and Es[iE][0] == tm:
            L, R, C = Es[iE]
            heappush(PQ, (dist+C, R))
            iE += 1

    return dists[-1]


print(solve())