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
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

n,m = map(int,readline().split())
chk = []
for i in range(m):
  l,r,c = map(int,readline().split())
  chk.append((l-1,r-1,c))
  
chk.sort()
class SegmentTree:
    def __init__(self, n, ele, segfun):
        self.ide_ele = ele
        self.segfun = segfun
        self.n = n
        self.N0 = 1 << n.bit_length()
        self.data = [self.ide_ele] * (self.N0 * 2)

    def update(self, l, r, val):
        l += self.N0
        r += self.N0
        while l < r:
            if l & 1:
                self.data[l] = self.segfun(self.data[l], val)
                l += 1
            if r & 1:
                self.data[r - 1] = self.segfun(self.data[r - 1], val)
                r -= 1
            l //= 2
            r //= 2

    def query(self, i):
        i += len(self.data) // 2
        ret = self.data[i]
        while i > 0:
            i //= 2
            ret = self.segfun(ret, self.data[i])
        return ret

S = SegmentTree(n,10**14,lambda a,b: min(a,b))
S.update(0,1,0)
for l,r,c in chk:
  a = S.query(l)
  S.update(l,r+1,a+c)
  
ans = S.query(n-1)
if ans == 10**14:
  print(-1)
else:
  print(ans)