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 collections import deque
import heapq

N,M = map(int,input().split())
LRC2 = []

for i in range(M):
    
    L,R,C = map(int,input().split())
    L -= 1
    R -= 1
    LRC2.append([L,R,C])

LRC2.sort()

LRC = deque([])

for i in LRC2:
    LRC.append(i)

q = []

for i in range(N):

    while len(LRC) > 0 and LRC[0][0] == i:
        now = LRC.popleft()
        L = now[0]
        C = now[2]
        R = now[1]

        if L == 0:
            heapq.heappush(q,[C,R])
            continue

        while len(q) > 0 and q[0][1] < i:
            heapq.heappop(q)

        if len(q) > 0:
            heapq.heappush(q,[C + q[0][0] , R])

    #print (LRC,q)


while len(q) > 0 and q[0][1] < N-1:
    heapq.heappop(q)

#print (q)

if len(q) > 0:
    print (q[0][0])

else:
    print (-1)