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:
n,m = map(int, input().split())
link = [[] for _ in range(n)]
for i in range(m):
    a,b,cost = list(map(int,input().split()))
    link[a-1].append([b-1,cost])
    link[b-1].append([a-1,cost])

for i in range(n-1):
    link[i+1].append([i,0])

from heapq import heappush, heappop,heappushpop,heapify
def dks(g,start,num_v):
    INF=float('inf')
    visited = set()
    hq = []
    heappush(hq, (0,start))
    cost = [INF] * num_v
    while hq:
        shortest, i = heappop(hq)
        if i in visited:
            continue
        visited.add(i)
        cost[i] = shortest
        for j, t in g[i]:
            if j in visited:
                continue
            heappush(hq, (shortest + t, j))
    return cost

ans=dks(link,0,n)
if ans[-1]!=float("inf"):
    print(ans[-1])
else:
    print(-1)