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
sys.setrecursionlimit(10 ** 7)

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

E = sorted(E)

# N_はN以上の2べき数
N_ = 2**(len(bin(N))-2)
INF = 10**15 # 10**10 
seg = [INF] * (2*N_-1)

# k番目(0index)をaに更新
def update(k, a):
    k += N_-1
    seg[k] = a

    while k > 0:
        k = (k-1)//2
        seg[k] = min(seg[k*2+1], seg[k*2+2])

# 開区間！！！[a, b)の最小値を求める
def query(a, b, k, l, r):
    if r <= a or b <= l:
        return INF
    if a <= l and r <= b:
        return seg[k]
    else:
        vl = query(a, b, k*2+1, l, (l+r)//2)
        vr = query(a, b, k*2+2, (l+r)//2, r)
        return min(vl, vr)



# 初期化
update(0, 0)

for i in range(M):
    new = query(E[i][0], E[i][1], 0, 0, N_) + E[i][2]
    if new < seg[E[i][1] + N_-1]:
        update(E[i][1], new)

if seg[N-1+N_-1] == INF:
    print(-1)
else:
    print(seg[N-1+N_-1])