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:
NN = 17
MI = [1<<100] * ((1<<NN+1)-1)
def update(a, x):
    i = (1<<NN) - 1 + a
    MI[i] = min(MI[i], x)
    while True:
        i = (i-1) // 2
        MI[i] = min(MI[2*i+1], MI[2*i+2])
        if i == 0:
            break

def rangemin(a):
    l = a + (1<<NN)
    r = ((1<<NN+1)-2)
    mi = 1<<100
    while l < r:
        if l%2:
            mi = min(mi, MI[l-1])
            l += 1
        if r%2:
            r -= 1
            mi = min(mi, MI[r-1])
        l >>= 1
        r >>= 1
    return mi

N, M = map(int, input().split())
X = []
for _ in range(M):
    l, r, c = map(int, input().split())
    X.append((l, r, c))

X = sorted(X)
update(1, 0)
for l, r, c in X:
    mi = rangemin(l)
    update(r, mi + c)

ans = MI[(1<<NN) - 1 + N]
print(ans if ans < 1<<100 else -1)