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
N,M = map(int,input().split())
LRC = [tuple(map(int,input().split())) for i in range(M)]
LRC.sort()

INF = float('inf')
class SegTreeMin:
    def __init__(self,arr):
        n = 1
        while n < len(arr):
            n *= 2
        self.n = n
        nodes = [INF]*(2*n-1)
        nodes[n-1:n-1+len(arr)] = arr
        for i in range(n-2,-1,-1):
            nodes[i] = min(nodes[2*i+1],nodes[2*i+2])
        self.nodes = nodes

    # thanks
    # https://smijake3.hatenablog.com/entry/2018/11/03/100133
    def update(self,i,val):
        i += self.n-1
        self.nodes[i] = val
        while i >= 0:
            i = (i - 1) // 2
            self.nodes[i] = min(self.nodes[2*i+1], self.nodes[2*i+2])

    def query(self,l,r):
        L = l + self.n; R = r + self.n
        s = INF
        while L < R:
            if R & 1:
                R -= 1
                s = min(s, self.nodes[R-1])
            if L & 1:
                s = min(s, self.nodes[L-1])
                L += 1
            L >>= 1; R >>= 1
        return s

segt = SegTreeMin([0] + [INF]*N)
for l,r,c in LRC:
    mn = segt.query(l-1,r-1)
    org = segt.query(r-1,r)
    if org > mn+c:
        segt.update(r-1, mn+c)

ans = segt.query(N-1,N)
print(-1 if ans==INF else ans)